The brightest nova of the century blasted lithium into space at 1.2 million mph (2 million km/h), new research reveals, cracking a long-standing mystery about the chemical balance of the universe.
Nova Centauri 2013 materialized in the sky in December 2013, caused by a huge nuclear explosion on a white dwarf star. This formed a new point in the constellation Centaurus, visible to the naked eye. Now, new measurements from the European Southern Observatory’s (ESO) La Silla facility in Chile reveal that the explosion is ejecting the element lithium, the first time that element has been seen in a nova system. This may help explain the topsy-turvy lithium distribution within stars, according to ESO officials.
“Understanding the amounts of lithium observed in stars around us today in the universe has given astronomers headaches,” ESO officials wrote in a statement. “Older stars have less lithium than expected, and some younger ones up to 10 times more.” The amount of lithium ejected from Nova Centauri is small, less than 1 billionth the mass of Earth’s sun. But the element’s presence in the nova supports a hypothesis in astronomy that a particular class of younger stars could have been built partially from lithium shot out of older stars. This would explain the younger bodies’ higher levels of lithium.
“It is a very important step forward,” study co-author Massimo Della Valle, from INAF–Osservatorio Astronomico di Capodimonte, Naples, and ICRANet, Pescara, Italy, said in the statement. “If we imagine the history of the chemical evolution of the Milky Way as a big jigsaw, then lithium from novae was one of the most important and puzzling missing pieces. In addition, any model of the Big Bang can be questioned until the lithium conundrum is understood.”Della Valle and another co-author, Luca Pasquini, an astronomer at University of Bologna in Italy, have been searching for traces of lithium in novas for over 25 years, according to the statement.
The lead scientist, Luca Izzo from Sapienza University of Rome and ICRANet, is excited too, although newer to the chase, he said in the statement: “It is very exciting to find something that was predicted before I was born and then first observed on my birthday in 2013!”
Planetary Resources deployed its first spacecraft from the International Space Station last month, and the Washington-based asteroid-mining company aims to launch a series of increasingly ambitious and capable probes over the next few years.
The goal is to begin transforming asteroid water into rocket fuel within a decade, and eventually to harvest valuable and useful platinum-group metals from space rocks.
“We have every expectation that delivering water from asteroids and creating an in-space refueling economy is something that we’ll see in the next 10 years — even in the first half of the 2020s,” said Chris Lewicki, Planetary Resources president and chief engineer Chris Lewicki.
“After that, I think it’s going to be how the market develops,” Lewicki told Space.com, referring to the timeline for going after asteroid metals.
“If there’s one thing that we’ve seen repeat throughout history, it’s, you tend to overpredict what’ll happen in the next year, but you tend to vastly underpredict what will happen in the next 10 years,” he added. “We’re moving very fast, and the world is changing very quickly around us, so I think those things will come to us sooner than we might think.”
Planetary Resources and another company, Deep Space Industries, aim to help humanity extend its footprint out into the solar system by tapping asteroid resources. (Both outfits also hope to make a tidy profit along the way, of course.)
This ambitious plan begins with water, which is plentiful in a type of space rock known as carbonaceous chondrites. Asteroid-derived water could do far more than simply slake astronauts’ thirst, mining advocates say; it could also help shield them from dangerous radiation and, when split into its constituent hydrogen and oxygen, allow voyaging spaceships to fill up their fuel tanks on the go.
The technology to detect and extract asteroid water is not particularly challenging or expensive to implement, Lewicki said. Scientific spacecraft routinely identify the substance on celestial bodies, and getting water out of an asteroid could simply involve bagging up the space rock and letting the sun heat it up.
Carbonaceous chondrites also commonly contain metals such as iron, nickel and cobalt, so targeting these asteroids could allow miners to start building things off Earth as well. That’s the logical next step beyond exploiting water, Lewicki said.
The “gold at the end of the rainbow,” he added, is the extraction and exploitation of platinum-group metals, which are rare here on Earth but are extremely important in the manufacture of electronics and other high-tech goods.
“Ultimately, what we want to do is create a space-based business that is an economic engine that really opens up space to the rest of the economy,” Lewicki said.
Developing off-Earth resources should have the effect of opening up the final frontier, he added.
“Every frontier that we’ve opened up on planet Earth has either been in the pursuit of resources, or we’ve been able to stay in that frontier because of the local resources that were available to us,” Lewicki said. “There’s no reason to think that space will be any different.”
Planetary Resources isn’t mining asteroids yet, but it does have some hardware in space. The company’s Arkyd-3R cubesat deployed into Earth orbit from the International Space Station last month, embarking on a 90-day mission to test avionics, software and other key technology.
Incidentally, the “R” in “Arkyd-3R” stands for “reflight.” The first version of the probe was destroyed when Orbital ATK’s Antares rocket exploded in October 2014; the 3R made it to the space station aboard SpaceX’s robotic Dragon cargo capsule in April. [Antares Rocket Explosion in Pictures]
Planetary Resources is now working on its next spacecraft, which is a 6U cubesat called Arkyd-6. (One “U,” or “unit,” is the basic cubesat building block — a cube measuring 4 inches, or 10 centimeters, on a side. The Arkyd-3R is a 3U cubesat.)
The Arkyd-6, which is scheduled to launch to orbit in December aboard SpaceX’s Falcon 9 rocket, features advanced avionics and electronics, as well as a “selfie cam” that was funded by a wildly successful Kickstarter project several years ago. The cubesat will also carry an instrument designed to detect water and water-bearing minerals, Lewicki said.
The next step is the Arkyd 100, which is twice as big as the Arkyd-6 and will hunt for potential mining targets from low-Earth orbit. Planetary Resources aims to launch the Arkyd-100 in late 2016, Lewicki said.
After the Arkyd 100 will come the Arkyd 200 and Arkyd 300 probes. These latter two spacecraft, also known as “interceptors” and “rendezvous prospectors,” respectively, will be capable of performing up-close inspections of promising near-Earth asteroids in deep space.
If all goes according to plan, the first Arkyd 200 will launch to Earth orbit for testing in 2017 or 2018, and an Arkyd 300 will launch toward a target asteroid — which has yet to be selected — by late 2018 or early 2019, Lewicki said.
“It is an ambitious schedule,” he said. But such rapid progress is feasible, he added, because each new entrant in the Arkyd series builds off technology that has already been demonstrated — and because Planetary Resources is building almost everything in-house.
“When something doesn’t work so well, we don’t have a vendor to blame — we have ourselves,” Lewicki said. “But we also don’t have to work across a contractural interface and NDAs [non-disclosure agreements] and those sorts of things, so that we can really find a problem with a design within a week or two and fix it and move forward.”
For its part, Deep Space Industries is also designing and building spacecraft and aims to launch its first resource-harvesting mission before 2020, company representatives have said.
Extracting and selling asteroid resources is in full compliance with the Outer Space Treaty of 1967, Lewicki said.
But there’s still some confusion in the wider world about the nascent industry and the rights of its players, so he’s happy that the U.S. Congress is taking up the asteroid-mining issue. (The House of Representatives recently passed a bill recognizing asteroid miners’ property rights, and the Senate is currently considering the legislation as well.)
“I think it’s more of a protection issue than it is an actual legal issue,” Lewicki said. “From a lawyer’s interpretation, I think the landscape is clear enough. But from an international aspect, and some investors — I think they would like to see more certainty.”
Now researchers have found that silica-rich rock much like the continental crust on Earth may be widespread at the site where Curiosity landed on Mars in August 2012.
“Mars is supposed to be a basalt-covered world,” study lead author Violaine Sautter, a planetary scientist at France’s Museum of Natural History in Paris, told Space.com. The findings are “quite a surprise,” she added.
Sautter and her colleagues analyzed data from 22 rocks probed by Curiosity as the six-wheeled robot wandered ancient terrain near Gale Crater. This 96-mile-wide (154 kilometers) pit formed about 3.6 billion years ago when a meteor slammed into Mars, and the age of the rocks from this area suggests they could help shed light on the earliest period of the Red Planets, scientists said.
The 22 rocks the researchers investigated were light-colored, contrasting with the darker basaltic rock found in younger regions on Mars. They probed these rocks using the rock-zapping laser called ChemCamon Curiosity, which analyzes the light emitted by zapped materials to determine the chemistry of Martian rocks.
The scientists found these light-colored rocks were rich in silica. A number of these were similar in composition to some of Earth’s oldest preserved continental crust.
Sautter noted that recent orbiter and rover missions had also spotted isolated occurrences of silica-rich rock. The researchers suggest these silica-rich rocks might be widespread remnants of an ancient crust on Mars that was analogous to Earth’s early continental crust and is now mostly buried under basalt.
The researchers added that the early geological history of Mars might be much more similar to that of Earth than previously thought. Future research could investigate whether the marked differences between Mars’ smooth northern hemisphere and rough, heavily cratered southern hemisphere might be due to plate tectonics, Sautter said.
The scientists detailed their findings online Monday (July 13) in the journal Nature Geoscience.
A heavyweight black hole in the heart of a distant galaxy has the mass of 140 million suns, according to new measurements. A vivid video by the National Radio Astronomy Observatory describes how researchers “weighed” the black hole at the center of the barred spiral galaxy NGC 1097.
Many galaxies have huge black holes in their centers, and these objects affect the galaxies’ growth and evolution. The galaxy NGC 1097 is 47 million light-years away from Earth, too far to determine the mass of its central black hole by the movement of the stars around it. But by tracking the movements of two types of molecular gases around the galaxy’s center, researchers using the Atacama Large Millimeter/submillimeter Array in Chile (ALMA) were able to work backward and figure out the black hole’s gravitational pull.
The ALMA telescopes tracked the radiation emitted from the two gases, hydrogen cyanide and formyl cation, as they swirled around the galaxy. The gases don’t interact strongly with environmental conditions within the galaxy, such as ionized gas flowing inward or outward. This means the gases paint an accurate picture of the effects of gravity’s pull alone. With just two hours of observational data, the researchers learned enough about the distribution and velocities of those gases to fit them to a model and calculate the pull of the galaxy’s core black hole.
The mass of a central black hole affects the physical properties of its host galaxy, and recent work has shown that those effects are different for different types of galaxies, study lead author, Kyoko Onishi, a doctoral student at the SOKENDAI (The Graduate University for Advanced Studies) in Japan, said in a statement. To understand those effects, Onishi said it’s important to measure the mass of these central black holes in various galaxy types.
Because of the quick precision measurements, “ALMA will enable us to observe a large number of galaxies in a practical length of time,” added Onishi, who is doing her research at the National Astronomical Observatory of Japan (NAOJ).
A Mars-size planet about 200 light-years from our solar system has turned out to be the lightest known alien world orbiting a normal star, researchers say.
Astronomers made the discovery after measuring the size and mass of the baking-hot planet, named Kepler-138 b, which orbits a red dwarf star called Kepler-138. Mars is only 53 percent the size of the Earth (or just about half the size), so Kepler-138 b is smaller than the Earth.
In the past couple of decades, astronomers have confirmed the existence ofmore than 1,800 exoplanets, or planets orbiting a star other than our sun. However, it’s more difficult for scientists to calculate the masses of small, rocky planets like Mars or Mercury than for large, gaseous worlds such as Jupiter or Saturn. Scientists measure the masses of exoplanets by looking at how strongly their gravitational fields tug on their stars; small planets have small masses, and their weak tugs on their stars are more difficult for astronomers to detect. As such, few Earth-size exoplanets have had their masses measured. [The Smallest Known Alien Planets in Pictures]
In this new study, astronomers investigated Kepler-138, a cold, dim red dwarf star with a mass about half that of the sun. Kepler-138 is located about 200 light-years from Earth, in the constellation Lyra.
Kepler-138 “is more than 10 million times further away from us than our sun,” study lead author Daniel Jontof-Hutter, an astronomer at Pennsylvania State University in University Park, told Space.com.
The star Kepler-138 is home to three exoplanets, prior research has confirmed by detecting the slight dimming of the star’s light that occurs whenever one of these worlds crosses in front of it. Each of these two planets — Kepler-138 c and Kepler-138 d — is about 1.2 times as wide as Earth. The third, Kepler-138 b, is a little more than half as wide as Earth, making it about the size of Mars.
“Kepler-138 b has the same apparent size to us as a golf ball 10 million kilometers [6.2 million miles] away,” Jontof-Hutter said.
These three exoplanets orbit very close to their star. Kepler-138 b takes a little more than 10 days to complete its orbit, Kepler-138 c requires nearly 14 days and Kepler-138 d needs about 23 days.
Using NASA’s Kepler spacecraft, the researchers looked at how the gravitational tug-of-war among these exoplanets influenced the lengths of their orbits. Because the strength of a planet’s gravitational pull is directly related to its mass, the scientists were able to weigh all three of these planets.
The astronomers found that the mass of the Mars-size inner planet, Kepler-138 b, is about one-fifteenth, or 6.7 percent, of Earth’s, making it about two-thirds the mass of Mars.
“Kepler-138 b is the first exoplanet smaller than Earth to have both its size and its mass measured,” Jontof-Hutter said.
The least massive known alien world may be the exoplanet PSR B1257+12 b, which has an estimated mass only about one-fiftieth, or 2 percent, that of Earth. However, that world does not orbit a normal star, but instead circles a pulsar — a dense, rapidly spinning remnant of a supernova explosion.
Knowing the mass and width of Kepler-138 b helped the researchers calculate its density, which they found is about two-thirds that of Mars, suggesting it has a purely rocky composition.
Although Kepler-138 b may be similar in mass and width to Mars, it is so much closer to its star, and thus hotter, meaning it is likely very different from Mars, Jontof-Hutter said. “In fact, all three planets orbiting Kepler-138 are likely too hot to retain liquid water,” Jontof-Hutter said. On the outermost planet, surface temperatures are about 250 degrees Fahrenheit (120 degrees Celsius), while those on the innermost planet are about 610 degrees F (320 degrees C).
Kepler-138 c and Kepler-138 d have masses 197 percent and 64 percent of Earth’s, respectively.
This finding opens up the study of rocky alien planets smaller than Earth, Jontof-Hutter said.
“The enormous variety of exoplanets that have been discovered by Kepler show us that systems like our own solar system are probably not the norm, and we don’t know why,” Jontof-Hutter said. Analyzing more exoplanets “will give us clues about how planets form and enable us to learn how common systems like are own really are.”
The scientists detailed their findings in the June 18 issue of the journal Nature.
Methane, a potential sign of primitive life, has been found in meteorites from Mars, adding weight to the idea that life could live off methane on the Red Planet, researchers say.
This discovery is not evidence that life exists, or has ever existed, on Mars, the researchers cautioned. Still, methane “is an ingredient that could potentially support microbial activity in the Red Planet,” study lead author Nigel Blamey, a geochemist at Brock University in St. Catharines, Ontario, Canada, told Space.com.
Methane is the simplest organic molecule. This colorless, odorless, flammable gas was first discovered in the Martian atmosphere by the European Space Agency’s Mars Express spacecraft in 2003, and NASA’s Curiosity rover discovered a fleeting spike of methane at its landing site last year.
Much of the methane in Earth’s atmosphere is produced by life, such as cattle digesting food. However, there are ways to produce methane without life, such as volcanic activity.
To shed light on the nature of the methane on Mars, Blamey and his colleagues analyzed rocks blasted off Mars by cosmic impacts that subsequently crash-landed on Earth as meteorites. About 220 pounds (100 kilograms) of Martian meteorites have been found on Earth.
The scientists focused on six meteorites from Mars that serve as examples of volcanic rocks there, collecting samples about one-quarter of a gram from each — a little bigger than a 1-carat diamond. All the samples were taken from the interiors of the meteorites, to avoid terrestrial contamination.
The researchers found that all six released methane and other gases when crushed, probably from small pockets inside.
“The biggest surprise was how large the methane signals were,” Blamey said.
Chemical reactions between volcanic rocks on Mars and the Martian environment could release methane. Although the dry thin air of Mars makes its surface hostile to life, the researchers suggest the Red Planet is probably more habitable under its surface. They noted that if methane is available underground on Mars, microbes could live off it, just as some bacteria do in extreme environments on Earth.
“We have not found life, but we have found methane that could potentially support microbes in the subsurface,” Blamey said.
Blamey now hopes to analyze more Martian meteorites. He and his colleagues detailed their findings online today (June 16) in the journal Nature Communications.
As NASA’s New Horizons spacecraft glides its way to the cold outer reaches of our solar system to take the first-ever up-close look at Pluto, the time is right to revise the International Astronomical Union (IAU)’s 2006 definition of a planet, which resulted in Pluto’s “demotion” from planet to ambiguous dwarf-planet status.
For those unfamiliar with the issues that led to that highly controversial decision, here’s a quick recap: It started with Pluto itself, discovered on Feb. 18, 1930, by Clyde Tombaugh, a young American astronomer working at Lowell Observatory in Flagstaff, Arizona. Pluto turned out to be rather unlike the other eight large objects orbiting the sun. Pluto is much smaller than Mercury, and only two-thirds the size of Earth’s moon. Its orbit is tilted and eccentric, crossing Neptune’s. No other planet acted like this. In 2000, astronomers found other objects orbiting the sun in the deep outer solar system, with qualities very much like Pluto’s. They were given names like Sedna , Quaoar, Ixion, Varuna, Makemake and Haumea . Many were close (but not quite equal) to Pluto in size. All of them had tilted, eccentric orbits; quite a few of those orbits crossed Neptune’s.
The tipping point came in 2005. California Institute of Technology astronomer Mike Brown, along with Chad Trujillo of Gemini Observatory and David Rabinowitz of Yale University, discovered a new massive body in the solar system. This new body, which astronomers latter dubbed Eris, was particularly noteworthy: Not only did it possess a moon, but at the time, it was estimated to be larger than Pluto. Subsequent observations revealed that Eris and Pluto are nearly identical in size, though Pluto is likely a few kilometers larger. Initially, Brown had named the newly discovered body Xena (after the protagonist of the eponymous TV show, with a sneaky Planet X reference). Although the name Xena didn’t stick, the IAU later officially — and aptly — christened it Eris after the Greek goddess of chaos and discord.
So, it seemed quite clear that if Pluto was our solar system’s ninth planet, then Eris should be its 10th. And if Eris and Pluto were planets, why shouldn’t Makemake and Haumea be considered planets as well? And what if there were even bigger objects out there to be discovered? Why shouldn’t the solar system have 15 planets, or 40? (Can you imagine the mnemonic device that would be required to remember 40 planets in the solar system?!)
For all who were in support of granting planet status to these objects, an equally adamant camp insisted that none of these objects, including Pluto, deserved to be called planets, and that our solar system contained only eight objects worthy of planet status. Neptune would be the last and final.
A worsening problem
With the intention of solving the debate once and for all, members of the IAU met in 2006. They spent days debating how to establish unambiguous definitions for the objects in our solar system. In the end, Resolution 5A was born:
The IAU therefore resolves that planets and other bodies in our solar system, except satellites, be defined into three distinct categories in the following way:
(1) A planet is a celestial body that (a) is in orbit around the sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
(2) A dwarf planet is a celestial body that (a) is in orbit around the sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape , (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
(3) All other objects, except satellites, orbiting the sun shall be referred to collectively as small solar-system bodies.
These are, to put it bluntly, terrible definitions. Despite its goal of providing unambiguous definitions, Resolution 5A actually contains the kind of ambiguity that most scientific organizations would protest. It adds confusion, resolves little and makes nobody happy.
So how did that become the official definition of a planet? A very strange vote. If you think low voter turnout is limited to politics, consider this: Only about 4 percent of IAU members were present for the vote on Resolution 5A. But it was travel schedules, not apathy, that caused this abysmal turnout. You see, the vote took place on the last day of the IAU meeting, when many people had to leave to catch flights back home — 424 astronomers were present, even though IAU membership in 2006 was just more than 10,000. As a result, Pluto lost the status it had enjoyed for more than 80 years and became a dwarf planet overnight. [Pluto Demoted: No Longer a Planet in Highly Controversial Definition]
The term “dwarf planet” itself causes confusion. You often hear people say Pluto is still a planet but that it just happens to be a dwarf planet now. But despite the name, the IAU does not consider a dwarf planet a planet — unlike a dwarf star, which is still a star, or a dwarf galaxy, which is still a galaxy. So much for eliminating ambiguity! But just the conflicting use of the word planet isn’t the most unclear part of the resolution.
Credit: Made with the Pluto Safari app for iOS and Android.
Picking apart Resolution 5A
Let’s dissect resolution 5A “Definition of ‘planet’”, one of six IAU Resolutions that were passed at the Closing Ceremony of the General Assembly in 2006.
*Nearly round shape. There is an element of something good here. We all intuitively feel that a planet should be round, or nearly so. But what is “nearly”? How lumpy and bumpy must an object be to no longer qualify as a planet or a dwarf planet? How smooth must the “ball” be? The Earth, which we all agree is a planet, is nearly round on some scales, but on others, it’s not. If you’re standing in the bottom of the Grand Canyon, the Earth isn’t even close to nearly round.
*Cleared the neighborhood. I’ve tried to wrap my head around this phrase for years, tried to convince myself that it makes sense — but I just can’t swallow it. The IAU is trying to express that, in addition to being round, a planet should be the dominant gravitational force in its local region of the solar system. That’s not an unreasonable position. Certainly the Earth and Jupiter are the dominant objects in their local regions. Neptune surely is, too. Even though Pluto’s orbit crosses Neptune’s, Neptune forces Pluto into something called a 3:2 resonance (for every three times Neptune goes around the sun, Pluto goes around twice), preventing collision. But have any of these planets actually “cleared the neighborhood” around their orbits? No. Pluto is still clearly in Neptune’s “neighborhood.” For that matter, Jupiter has two well-known groups of asteroids, the Trojans, which lead and follow Jupiter along in its orbit. For that matter, the Earth hasn’t quite “cleared the neighborhood” around its orbit, either, to which anyone who saw the near-Earth asteroids that entered Earth’s atmosphere near Chelyabinsk, Russia, on Feb. 15, 2013, or Tunguska, Siberia, on June 30, 1908, can attest. So are Earth, Jupiter and Neptune the dominant gravitational objects in their local neighborhoods? Yes, clearly. Have they cleared their neighborhoods? No. Not by a long shot.
Other scientists have weighed in on the matter. Alan Stern, principal investigator for the New Horizons mission to Pluto, made it clear he disagrees with the IAU resolution. “Any definition that allows a planet in one location but not another is unworkable. Take Earth. Move it to Pluto’s orbit, and it will be instantly disqualified as a planet,” Stern said.
The biggest problem with the IAU’s planet definition is that it replaces an already-ambiguous concept (“What is a planet?”) with three more ambiguous concepts, (“nearly round,” “cleared” and “neighborhood”). Indeed, the only definitive part of the IAU resolution on which everyone can agree is the first part: (1) A planet is in orbit around the sun. It’s why the moon is not a planet. My 6-year-old niece intuitively understands this. It’s the only part of the IAU definition I would keep.
The way out
Let’s look at some other kinds of definitions that are clear and unambiguous.
*International boundaries. It’s well understood that the portion of North America north of 49 degrees, between the Canadian provinces of British Columbia, Alberta, Saskatchewan and Manitoba, and the U.S. states of Washington, Idaho, Montana, North Dakota and Minnesota, is called Canada, and the portion below that latitude is called the United States. There’s no physical demarcation — no river, no mountain range — along the 49th parallel. There’s no subtle change in vegetation or geological structure. But there is a hard, sharp, clearly defined, well-understood boundary that unambiguously answers the question, “What is Canada?” It’s the country north of the 49th parallel. It passes the 6-year-old-niece test.
*Constellation boundaries. Back in 1888, the IAU defined an intricate set of boundary lines in the sky, precisely outlining the groups of stars that were commonly referred to as constellations. It also declared that there would be 88 of these constellations. Lines were chosen carefully, to respect traditional choices about which star might lie in which constellation, and in the end, the definitions were clear. There is no ambiguity about which particular point in the sky falls within which constellation. And, you can tell precisely when a moving celestial object (like Pluto) might cross from one constellation to another. It’s an arbitrarily agreed upon but well-defined system of definitions that has served the astronomical community well for more than 100 years.
*The Karman line that defines the edge of space. Where does the Earth’s atmosphere end and outer space begin? Clearly, there is no physical boundary. There is no bubble holding the atmosphere that one must pierce on one’s way to the International Space Station. The air just gets thinner and thinner until you can ignore it. But in reality, air molecules continue to exist, albeit in smaller numbers, out to an altitude of many thousands of kilometers and beyond — indeed, some of these air molecules may have made it as far as Pluto by now! However, since the early days of manned spaceflight, a near-universally accepted definition is that space begins at an altitude of 100 kilometers (62 miles). In fact, this definition is accepted by the Fédération Aéronautique Internationale (FAI), an international standard-setting body for aeronautics and astronautics. Pilots who’ve flown higher than 100 km have officially earned the title of astronaut. It’s another arbitrary, but widely accepted convention that is clear, unambiguous and easily passes the 6-year-old comprehension test.
What the IAU should have done in 2006, and could easily do moving forward, is to crystallize the definition of the word “planet” as unambiguously as it defined the boundaries of the constellations in 1888. Yes, that definition would have been arbitrary, and yes, the actual physical objects themselves would gradually transition from larger to smaller, and don’t care in the least what we choose to call them. But the IAU could have chosen a definition that resolves the debate in a far more satisfying manner than it actually did.
Credit: Made with the Pluto Safari app for iOS and Android
The 1,000-km rule
So, what would be a better definition for the objects in the solar system?
(1) A “planet”  is a celestial body that (a) is in orbit around the sun, and (b) has a maximum surface radius greater than 1,000 km (620 miles).
(2) All other objects, except satellites, orbiting the sun shall be referred to collectively as small solar-system bodies.
“But that’s completely unscientific,” you may say. “Why 1,000 km? Why not 1,200, or 750?”
I submit that the precise definition of a planet as an object with a radius of at least 1,000 km is no less scientific than the definition of a kilometer as being a unit of distance equal to 1,000 m, or a degree being 1/360 of a circle.
And there are other reasons why the 1,000-km definition is more scientific than it might seem at first. But let’s put that aside momentarily. Instead, let’s see what would have happened if the IAU had adopted this definition.
Here is a list of the largest known objects orbiting the sun, and their radii in kilometers:
Object Radii (km)
Jupiter: 69,911 km (43,441 miles)
Saturn: 58,232 km (36,184 miles)
Uranus: 25,362 (15,759 miles)
Neptune: 24,622 (15,299 miles)
Earth: 6,378 (3,963 miles)
Venus: 6,052 (3,761 miles)
Mars: 3,390 (2,106 miles)
Mercury: 2,440 (1,516 miles)
Pluto: 1,184 (736 miles)
Eris: 1,163 (723 miles)
Makemake: 715 (444 miles)
Haumea: 620 (385 miles)
Quaoar: 555 (345 miles)
Sedna: 498 (309 miles)
Ceres: 475 (295 miles)
Orcus: 458 (285 miles)
By the 1,000-km definition, all eight classical planets would remain planets. So would Pluto. And we’d add Eris. The solar system would have exactly 10 planets, a number that is deeply satisfying to two-handed, five-fingered humans who’ve been practicing base-10 mathematics for thousands of years. The “Plutophile” camp, fond of keeping Pluto’s planetary status for historical reasons, would retain its dignity. And elevating Eris to a first-class planet would be an honorable nod to the cutting-edge astronomers whose work led to a need for this new definition in the first place.
And finally, the 1,000-km rule, like any good arbitrary rule, actually does a pretty good job of respecting the underlying physical phenomena that it purports to define. Planets are made of physical materials like rock, metal, gas and ice. They may come in different proportions, but those materials all respect the same physical laws. When you put together a lump of rock, metal or ice, in any proportion, certain things start to happen as that lump approaches 1,000 km in radius. The materials will pull together under the force of their own gravity. Solid rock will start to deform. Ice, even frozen hard as granite at the edge of the solar system, will slowly flow. There is no known substance that can resist the force of its own gravity when made into a lump with a 1,000-km radius. Any object, made of any substance, of approximately that size, will eventually flow under action of its own gravity into a shape that is “nearly round” when viewed from far away. The 1,000-km radius just happens to describe something that naturally takes place for objects of a certain size and results in what we all intuitively want a planet to look like.
And for space enthusiasts, there’s one more benefit to my proposed definition. While we’re all looking forward to the New Horizons Pluto flyby, there’s also a certain sadness to knowing that, after Pluto, there will be no more planets in our solar system to explore. If our solar system has 10 planets, that’s no longer true. As far away and difficult as it was to reach Pluto, it will be even more difficult to reach Eris. It’s another frontier, another first and another project to fund. That prospect alone should give the scientific community a reason to rethink and resolve Resolution 5A.
Mars is a large enough planet that astrobiologists looking for life need to narrow the parameters of the search to those environments most conducive to habitability.
NASA’s Mars Curiosity mission is exploring such a spot right now at its landing site around Gale Crater, where the rover has found extensive evidence of past water and is gathering information on methane in the atmosphere, a possible signature of microbial activity.
But where would life most likely gain energy from its surroundings? One possibility is in an environment that includes “green rust,” a partially oxidized iron mineral. A fully oxidized iron “rust” — one exposed to oxidation for long enough — turns orangey-red, similar to the color of Mars’ regolith. When oxidization is incomplete, however, the iron rust is greenish.
This means that there are two different “redox states,” or types of iron with different numbers of electrons in the same mineral. This difference between the two iron redox states could allow the mineral to take in or give up electrons and thus act as a catalyst, said Laurie Barge, a planetary scientist at NASA’s Jet Propulsion Laboratory. She studies hydrothermal vents, an area where chemical contrasts also fuel life.
“From an environmental science perspective, green rust can absorb and concentrate nutrients, and can also accept and donate electrons for life,” said Barge.
She is the lead author of related work that was presented at the American Geophysical Union’s Joint Assembly meeting in May 2015. Funding for this work comes from the Jet Propulsion Laboratory’s Icy Worlds team as part of the NASA Astrobiology Institute (NAI) element of the Astrobiology Program at NASA.
One major challenge in the search for life on Mars is that its surface is highly oxidized. On Earth, green rust generated in Barge’s lab oxidizes quickly when exposed to air, and its composition is changed in only an hour. However, the lack of oxygen on Mars makes this a slower process. It is likely that green rust occurs beneath the oxidized surface, perhaps only a centimeter or half-inch deep as revealed by Curiosity.
There are more probes on the way to Mars that will include drills. One of those will be NASA’s InSight lander, which is set to go to the Red Planet in 2016. Another is the European Space Agency’s ExoMars rover, expected to launch in 2018.
A major focus of current NASA missions on Mars is finding out where water has flowed in the past. NASA’s Curiosity, Opportunity and Spirit rovers have all found rocks that form in the presence of water, such as the red iron oxide mineral hematite, as well as select sulfates and clays. Further, several orbiting spacecraft have seen signs, such as the presence of gullies, in which water is thought to have once flowed on the surface.
Barge knows from her experiments that green rust forms when two contrasting solutions – one containing iron and one containing hydroxide – are mixed. On Earth, green rust has been found in such environments as non-oxygenated wet sediments and steel pipes that corrode in sea water.
Probing by laser
To detect green rust, Barge suggests using laser Raman spectroscopy, a technique which will be included on ESA’s ExoMars and NASA’s Mars 2020 missions. The technique involves directing a laser beam at a sample and then collecting and analyzing the light that is scattered from the spot to identify its molecular composition and structure. The scattered light contains fingerprint spectral features that allow us to determine the molecular makeup and mineralogy of the sample. Barge has teamed up with Pablo Sobron, a research scientist at the SETI Institute, an expert in laser-based spectroscopy applied to Mars exploration, to adapt the Raman technique for the detection and analysis of green rust.
But first, there needs to be a better understanding of where green rust will occur and how it can support habitability. The JPL Icy Worlds team (led by the Jet Propulsion Laboratory’s Isik Kanik) recently received a second five-year NASA Astrobiology Institute grant to study the habitability of icy worlds, including an investigation into how green rust might drive prebiotic chemistry, or chemistry that is a precursor to life.
“There’s a theory proposed by Michael Russell at JPL that green rust could have acted as a proto-enzyme to convert energy currencies on early Earth,” Barge said, referring to how lifeforms convert proton and electron gradients into chemical energy to drive metabolism and, thereby, life.
Green rust is especially interesting in this regard because it is a double layered hydroxide that can sandwich all sorts of interesting components relevant to life in between these layers, Barge added. These include phosphates, DNA, amino acids and proteins.
Dark matter is five times more plentiful in the universe than regular matter, but it does not emit, reflect or absorb light, making it not just dark but entirely transparent. But if dark-matter particles around black holes can produce gamma-rays (high-energy light), such emissions would give scientists a new way to study this mysterious material.
The process responsible for creating the gamma-rays is somewhat counterintuitive, because it seems to defy two common assumptions: that nothing can escape from a black hole and that there’s no such thing as a free lunch.
Jeremy Schnittman is a theoretical astrophysicist at the NASA Goddard Space Flight Center, and he’s beginning a project to look through data from the Fermi Gamma-ray Space telescope for signs of high-energy light around the edge of a black hole that might have been created by dark matter.
“We’re really just getting started on this part of the problem,” Schnittman said. “As a theoretical astrophysicist, I haven’t done a lot of data analysis in my career, so it’s a little bit of a learning curve for me. But fortunately I’m surrounded by people here at Goddard who are real experts at the Fermi data.”
Schnittman’s search for this dark-matter signal began with a computer program that he has been developing for about 10 years. It models in 3D the paths of particles as they zip through space near a black hole, while some of them get close enough to orbit around the black hole or fall in.
Just over a year ago, he decided to adjust the program to model dark-matter particles. The resulting video shows how the subatomic bits get caught up in the gravitational pull of the black hole and swirl around it in a region called the ergosphere (where all particles must orbit in the direction of the black hole’s spin). Some of the particles collide and destroy each other (also known as annihilation), and this produces a pair of gamma-rays.
These particles of light might normally fall into the black hole, helpless against its gravitational pull, were it not for something called the Penrose process.
In 1971, astrophysicist Roger Penrose showed that if two photons are created very close to a black hole, it’s possible for one of them to escape, while the other falls in. This flies counter to the commonly held idea that nothing can escape from a black hole, or at least nothing that goes past the “event horizon” — the point at which the gravitational pull is so strong that nothing, not even light, can ever exert enough force to get away.
According to the Penrose principle, the particles are not created beyond this point of no return, but under normal circumstances, it’s unlikely that either particle would have any means of getting away from the black hole. So the Penrose process still changes the fate of at least one particle, giving it an escape route.
In 2009, a group of researchers showed that the Penrose process could be applied to dark-matter particles that annihilate and form two gamma-rays. If dark-matter particles are annihilating near the surface of a black hole, telescopes on Earth could detect the escaping gamma-rays.
Schnittman’s work using the 3D computer model has shown many more paths that the particles can take, including some that are more likely to produce gamma-rays that can escape the black hole, and with even higher energies than had been previously predicted. A brief description of those results was published in the journal Physical Review Letters last December, and a longer description of the work has been accepted to the Astrophysical Journal.
With those results, Schnittman and his colleagues are now looking for this signal, although they said they expect it to be very dim compared to many other gamma-ray sources. The researchers are creating a list of target galaxies that have few gamma-ray sources and very massive black holes.
“The bigger the black hole, the bigger the signal,” Schnittman said. “It scales in a way that as your black hole [mass] goes up by a factor of 10, the expected signal goes way up, by something like a factor of 1,000.
“The first pass at observing this effect is almost certainly not going to yield an actual detection. But it will provide probably the strongest upper limit on this type of process that has ever been seen before — the idea of high-energy dark-matter particle reactions. Even that is progress.”
The particles that escape the black hole via the Penrose process not only go free, but they also leave with more energy than they started with. In fact, they have more energy than the pair of particles had combined. This, it would seem, is a free lunch.
Since Penrose’s original work, scientists have shown that not only does the escaping particle steal energy from its partner (essentially pushing off the other particle), but it also steals energy from the spinning black hole. Every Penrose particle that escapes slows the spin of the black hole by a very, very tiny amount.
(When he originally proposed the idea, Penrose wrote that this phenomenon could be used by an advanced society as an energy-producing garbage disposal, in which the garbage serves as the particle that falls into the black hole, producing a flux of high energy particles that escapes.)
Schnittman said he is reserved in his hopes for finding a dark-matter signal in the Fermi data. Not only will it be difficult to see such a small signal amid the noise of gamma-rays in the universe, but the existence of the signal also relies on a major unknown: whether or not dark-matter particles create gamma-rays when they annihilate.
The fact is, scientists don’t know what dark matter is made of, and they don’t know if dark-matter particles will annihilate in the way that Schnittman’s model predicts, if they do so at all. So if Schnittman did find a signal, it would mean a major breakthrough in the study of the nature of dark matter.
“That’s Nobel Prize kind of stuff,” Schnittman said. “It’s a long shot, but it would be a tremendous payoff if we found actual confirmation of dark-matter annihilation.”
Saturn’s icy moon Enceladus is looking better and better as a potential abode for alien life.
Chemical reactions that free up energy that could potentially support a biosphere have occurred — and perhaps still are occurring — deep within Enceladus’ salty subsurface ocean, a new study suggests.
This determination comes less than two months after a different research team announced that active hydrothermal vents likely exist on Enceladus’ seafloor, suggesting that conditions there could be similar to those that gave rise to some of the first lifeforms on Earth.
Astrobiologists regard the 314-mile-wide (505 kilometers) Enceladus as one of the solar system’s best bets to host life beyond Earth.
The satellite is covered by an icy shell, but it’s geologically quite active, as evidenced by the powerful geysers that blast continuously from its south polar region. These plumes contain significant amounts of water, which scientists think originates from a subsurface ocean.
Previous studies have suggested that this ocean is in contact with Enceladus’ rocky mantle, making possible all sorts of interesting chemical reactions. The new paper, published Wednesday (May 6) in the journal Geochimica et Cosmochimica Acta, further supports that notion.
The researchers studied mass-spectrometry measurements of the gases and ice grains in Enceladus’ plumes made by NASA’s Cassini spacecraft, which has been orbiting Saturn since 2004. The team used this information to develop a model that estimates the saltiness and pH of Enceladus’ plumes, and, by extension, the moon’s underground ocean.
The scientists determined that the ocean is likely salty and quite basic, with a pH of 11 or 12 — roughly equivalent to that of ammonia-based glass-cleaning solutions, but still within the tolerance range of some organisms on Earth. (The pH scale runs from 0 to 14. Seven is neutral; anything higher is basic, and anything lower is acidic.)
Enceladus’ subsurface sea contains dissolved sodium chloride (NaCl) — run-of-the-mill table salt — just as Earth’s oceans do, researchers said. But it’s full of sodium carbonate (Na2CO3), which is also known as washing soda or soda ash, as well.
So this alien water body is probably more similar to terrestrial “soda lakes,” such as Mono Lake in California, than it is to the Atlantic and Pacific oceans, study team members said.
Such inferences shouldn’t dishearten astrobiologists; a variety of lifeforms thrive in Mono Lake, including brine shrimp and many different types of microbe. And the new study provides other reasons to be optimistic about Enceladus’ life-hosting potential, researchers said.
For example, the team’s model suggests that the subsurface ocean’s high pH is generated by a process called serpentization, in which certain kinds of metallic rocks from Enceladus’ upper mantle are transformed into new minerals (including serpentine, hence the name) via interactions with water.
In addition to raising pH, serpentization results in the production of molecular hydrogen (H2) — a potential source of chemical energy for any lifeforms that may exist in the underground sea, researchers said.
”Molecular hydrogen can both drive the formation of organic compounds like amino acids that may lead to the origin of life, and serve as food for microbial life such as methane-producing organisms,” study lead author Christopher Glein, of the Carnegie Institution for Science in Washington, said in a statement.
“As such, serpentinization provides a link between geological processes and biological processes,” he added. “The discovery of serpentinization makes Enceladus an even more promising candidate for a separate genesis of life.”
Sunlight probably doesn’t flow through Enceladus’ underground sea, but any microbes that exist there may thus have access to two different sources metabolism-supporting energy sources — molecular hydrogen and the heat provided by hydrothermal vents.
More than 40,000 citizen stargazers have helped to classify over 2 million celestial objects and identify five never-before-seen supernovas, in a massive example of citizen science at work.
An amateur astronomy project of cosmic proportions, established by scientists at the Australian National University, asked volunteers to look through images taken by the SkyMapper telescope and search for new objects, with a particular focus on finding new supernovas.
The project was set up using the Zooniverse platform (run by the University of Oxford), which hosts many other citizen science projects, and which was promoted on the BBC2 TV series “Stargazing Live,” from March 18 to March 20. [Supernova Photos: Great Images of Star Explosions]
To participate in the project, volunteers signed up online and accessed the Zooniverse platform, which walked them through their tasks.
Zooniverse has hosted many space-related citizen science projects in the past, including hunts for alien planets, “space warp” galaxies and holes in cosmic clouds.
The participants were asked to look at star-filled patches of the night sky, taken by the SkyMapper telescope. The volunteers would look at images of the same region taken at different times, and search for changes that could indicate the presence of different celestial objects.
A supernova, for example, is a large star that has burned up most of its fuel and dies in a great explosion. A supernova eruption can briefly outshine all the light created by all the stars in an entire galaxy — so even a star that is normally too distant to see with a telescope may suddenly become visible if it explodes into a supernova. This means a SkyMapper volunteer might see a point of light appear where there previously was none.
“One volunteer was so determined to find a supernova that he stayed online for 25 hours. Unfortunately, he didn’t find one, but he did find an unusual variable star, which we think might explode in the next 700 million years or so,” Richard Scalzo, a researcher working with the SkyMapper telescope at the Australian National University (ANU) Research School of Astronomy and Astrophysics, said in a statement from ANU (a variable star is one that changes in brightness when observed from either, either due to changes in the star itself or something between the star and the observer). “It was a huge success. Everyone was really excited to take part.”
That excitement paid off, as the project required multiple volunteers. If one of the citizen scientists spotted a possible supernova or some other change in the sky images, then additional volunteers would examine that same region.
If the citizen observers confirmed a new object, then the professional scientists would do a more extensive background check in that region of the sky, Scalzo said in an email. After that, the scientists looked at the object’s spectra, a breakdown of the light the object emits. This can tell scientists all kinds of information about the object’s makeup and its history.
“Once we have at least one spectrum, we consider what other science we could do,” Scalzo said. “Type Ia supernovae can be used to study the expansion history of the universe and dark energy. Other kinds of supernovae can be used, singly or in large groups, to learn more about how different kinds of stars end their lives.”
Scalzo said the project required the assistance of so many human helpers because the computer programs need assistance. “Computers are very good at identifying supernova,” he said, “but you need a lot of data to train them.”
In other words, the scientists have to provide the computer program with lots of examples of what the supernova look like; it isn’t as simple as telling the computer to look for changes in the sky images.
“A few years ago, before SkyMapper was ready to take data, another group called the Palomar Transient Factory (PTF) partnered with the Zooniverse to allow volunteers to hunt for supernovae,” Scalzo said. “Over a few years, PTF found more than 500 real supernovae with the help of Zooniverse volunteers, and used the data to train a machine-learning algorithm to recognize supernovae more accurately than the volunteers could.”
The SkyMapper telescope has only identified 15 supernova, so Scalzo said there is still work to do to improve the programs.
The five newly discovered supernovas have already made their way into a cosmological study of dark energy by the SkyMapper scientists, but Scalzo said there is more work to be done before the results of that study are published. He added that there may be more work for citizen scientists to do with SkyMapper data in the future.
In the search for life beyond Earth, the mantra has usually been, “Follow the water.” But now, scientists say it may be possible for a waterless environment to give rise to alien life.
In a recent study, researchers at Cornell University proposed a formula for life that could thrive on Saturn’s largest moon, Titan. With its freezing temperatures, seas of liquid methane and toxic atmosphere devoid of any liquid water, it may seem unlikely that Titan could give rise to life. But in such environments, it may be possible for there to be methane-based, oxygen-free extraterrestrial life, the researchers said.
On Titan, temperatures of minus 292 degrees Fahrenheit (minus 180 degrees Celsius) would make it difficult for processes like metabolism and reproduction to occur. But the theorized cell membrane, which houses the cell’s organic matter, is composed of nitrogen instead of water, allowing it to do just that. [5 Bold Claims of Alien Life]
On Earth, living cells have a strong, permeable, water-based barrier called a lipid bilayer membrane. But that concept works only in environments with liquid water, so when astronomers are searching for life outside our solar system, they zoom in on small rocky exoplanets orbiting inside a star’s habitable zone — the band where liquid water can exist. But plenty of exoplanets (and even solar system moons) exist well outside this range, where liquid water can’t exist.
So astronomers have long been fascinated by nonaqueous life, and even the possibility that Titan may host methane-based life. Other than Earth, it is the only place in our solar system with liquid seas on its surface. It also hosts a mysterious process that consumes hydrogen, acetylene and ethane, the researchers said. All of these elements flow down from the atmosphere but never quite make it to the surface. So, could life be gobbling them up?
To investigate this possibility, Jonathan Lunine, an astronomer at Cornell University, collaborated with James Stevenson, a graduate student, and his adviser, Paulette Clancy, both of whom work at Cornell’s Chemical and Biomolecular Engineering Department.
“We’re not biologists, and we’re not astronomers — but we had the right tools,” Clancy said in a statement. “Perhaps it helped, because we didn’t come in with any preconceptions about what should be in a membrane and what shouldn’t. We just worked with the compounds that we knew were there and asked, ‘If this was your palette, what can you make out of that?’”
The researchers were able to model a cell that supports metabolism and reproduction but that’s constructed from nitrogen, carbon and hydrogen-based molecules — all of which are known to exist within Titan’s frigid seas. Like a lipid bilayer membrane here on Earth, it’s both rigid and flexible, controlling the transportation of materials in and out of the cell.
They named their theorized cell membrane an “azotosome.” (Azote is French for nitrogen, and lipsome is Greek for “lipid body,” so “azotosome” means “nitrogen body.”)
So far, the researchers have only shown that azotosomes could exist based on molecular simulations.
“Ours is the first concrete blueprint of life not as we know it,” Stevenson said. The next step will be to demonstrate in the laboratory how such membranes function in a methane environment. In the long run, scientists might also be able to model possible observable indicators of alien life.
If life does exist on Titan, it would demonstrate that methane, in addition to water, could be an indicator of life, and that life could more easily populate the cosmos.
Earlier this month, researchers made two big announcements: Saturn’s moon Enceladus likely harbors hot springs, and Jupiter’s huge satellite Ganymede apparently possesses a subsurface ocean that may contain more water than all of Earth does.
However, while the discovery makes Enceladus, which also has a subsurface ocean, even more intriguing to astrobiologists, Ganymede is still not a great bet for alien life, researchers say. [6 Most Likely Places for Alien Life in the Solar System]
Enceladus is the sixth-largest of Saturn’s moons, with a diameter of only about 314 miles (505 kilometers). Despite its tiny size, Enceladus has drawn a great deal of attention due to its erupting water geysers, first seen by NASA’s Cassini spacecraft in 2005. Now, scientists have found that Enceladus may have hot springs under its frozen crust. The discovery that the floor of its hidden ocean may be home to near-boiling temperatures is the first evidence of active hydrothermal vents beyond the oceans of Earth.
“This surely has implications regarding astrobiology, life-searching and all those kinds of topics,” said study author Hsiang-Wen Sean Hsu, a planetary scientist at the University of Colorado, Boulder.
Specifically, these new findings suggest that the conditions on Enceladus’ seafloor are similar to those found on Earth in a deep-sea field of hydrothermal vents known as Lost City in the Atlantic Ocean, which is home to a wide variety of animals, such as eels, snails, mussels, worms, shrimplike amphipods and flealike ostracods, said Gabriel Tobie, a planetologist at the University of Nantes in France.
Lost City consists of 196-foot-tall (60 meters) limestone chimneys that release alkaline fluid that is low in metals and lower than boiling temperature. In contrast, most other known hydrothermal vents on Earth give off metal-rich acidic fluid that is hotter than boiling temperature.
Alkaline hydrothermal vents might have been the birthplace of the first living organisms on the early Earth, supplying key nutrients and energy, Tobie said.
“For Enceladus, the new discovery of hot vents enhances its chance for life,” Tobie told Space.com.
NASA also announced that a salty ocean hides beneath the icy crust of Ganymede, the largest moon in the solar system. Scientists using NASA’s Hubble Space Telescope found that Ganymede’s ocean could harbor more water than is found on Earth. Ganymede’s sea may be about 60 miles (100 km) deep — 10 times the depth of Earth’s oceans.
However, this finding does not necessarily raise Ganymede’s chances for life, Tobie said.
“A major difference between Enceladus and Ganymede is the difference of pressure at the base of the ocean,” Tobie said. The pressure at the base of Enceladus’ ocean is rather low, at 50 to 100 bar — or about 50 to 100 times the atmospheric pressure of Earth at sea level. This low pressure permits water from circulating in underlying porous rocks, thus helping to drive chemical reactions that could lead life to emerge.
In contrast, the pressure at the base of Ganymede’s ocean is much higher — about 15,000 to 20,000 bar, Tobie said. Under such high pressure, not only is rock less porous, but water can form a kind of ice.
“A very thick layer of high-pressure ice more than 400 kilometers [250 miles] thick will form at the base of the ocean,” Tobie said. “Even if deep hot vents exist on Ganymede, the chance for life seems rather low due to the formation of this high-pressure ice layer.”
However, Ganymede is not the only watery moon of Jupiter. Prior research suggests that Europa, the fourth-largest moon of Jupiter, may possess both an ocean beneath its icy surface and hot springs.
“Like in Enceladus, the ocean in Europa would be directly in contact with the rock core, which will favor water-rock interactions and exchange of nutrients with the ocean,” Tobie said.
“Both Europa and Enceladus have a high astrobiological potential,” he added. “But for the moment, it is only a potential. Only future missions with in situ investigations will really answer if it is more than only a potential.”
Cosmic detectives are investigating a case of mistaken stellar identity: An exploding star that was once thought to be the oldest recorded nova — a nuclear explosion on the surface of a dead star — was more likely caused by the merger of two stars.
In 1670, a bright new star appeared in the constellation Cygnus, the Swan, and stayed there for two years — you can see the location of the new stars in this video. The short-lived star was grouped into the “nova” category, but over the last 30 years, astronomers have been questioning its identity.
A new research paper that examines the chemical makeup of the crime scene may be the final nail in the coffin. The researchers suggest that the so-called nova is instead the oldest example of another type of stellar explosion sometimes called a “red nova” — a somewhat newly-discovered phenomenon that scientists are still working to understand.
In 1670, a new star appeared just above the head of the swan that makes up the constellation Cygnus. Many astronomers took note of this newcomer, so its appearance and life span are well documented. It was dubbed Nova Vul 1670 —at the time, “nova” referred simply to any new star.
In the last 300 years, however, the word “nova” has taken on a much more specific and scientific meaning.
By today’s definition, a classic nova is an explosion that takes place on the surface of a white dwarf — the small, dense, nugget of leftover material from a star that has stopped burning. The white dwarf syphons material away from another nearby star, the pressure builds up on its surface and a nuclear reaction releases an incredible burst of energy. (Unlike Type Ia supernovas, which start in a similar fashion, the white dwarf in a nova is expected to survive through the explosion.)
Many things about CK Vulpeculae’s identity as a nova just don’t line up, said Tomasz Kaminski, a postdoctoral fellow at the European Southern Observatory.
For example, novas tend to burn in the sky for days — not years, as CK Vulpeculae did. Plus, the new star of 1670 didn’t disappear right away. After two years, it faded, then reappeared, then faded for good — which is very unusual for a nova, Kaminski said. And observations have shown that CK Vulpeculae’s temperature is much lower than that of a nova, where the radiation from the nuclear reaction continues to generate heat after the explosion is done, Kaminski said.
The new study, which is detailed in the March 23 edition of the journal Nature, may finally strip CK Vulpeculae of its “nova” title. Kaminski and his co-authors looked at the different molecules present in the wreckage of CK Vulpeculae, and found a profile that they say cannot be created by a classical nova.
But if isn’t a nova, then what is it?
In the new paper, Kaminski and his colleagues argue that CK Vulpeculae is a phenomenon with multiple names in scientific literature. They’ve been called red novas, red transients, luminous red transients and intermediate luminous optical transients (ILOTs), among others.
“People who study these red nova realized all the observations we have of these objects can be explained only if they explode as [an] effect of a collision and a merger of two stars,” Kaminski said.
The notion that a red nova could be a unique category of stellar explosion took hold in 2008, when astronomers watched two stars in a system orbit in toward each other and produce an explosion with the characteristics of a red nova, Kaminski said.
“Many of the novae we know from historical records could be this type; it’s just that people observe them during the outburst, and then no one really cared what happened with them,” Kaminski said. “And that’s why they didn’t realize maybe we’re dealing with some new phenomenon.”
Previous groups have suggested that CK Vulpeculae is a red nova. What Kaminski and his group have provided is the first look at the molecular profile of one of these objects, which he said is distinct from other stellar explosions. [Star Quiz: Test Your Stellar Smarts]
“This is a major step,” he said. The chemical profile shows the presence of molecules and isotopes that are strange compared to other types of stellar explosions, including classical novas, Kaminski said. In fact, the profile is actually somewhat unique among red nova, which may be a product of CK Vulpeculae’s age — perhaps something happens in these red novas over time that produces a unique bouquet of chemicals, he said.
The researchers made their observations with the submillimeter-wavelength Atacama Pathfinder Experiment (APEX) telescope and Effelsberg radio telescope.
Kaminski cautioned that scientists are still working to demonstrate that red novas are, in fact, the products of stellar mergers.
Noam Soker, an astrophysicist at the Technion Israel Institute of Technology, was one of the scientists who previously suggested that CK Vulpeculae was a red nova. He and some of his colleagues have theorized that red novas are not the result of suddenly stellar mergers but rather are produced by the gradual accretion of matter from one star to another. He and Kaminski said one thing that would help clarify the cause of a red nova would be observations inside the clouds of debris, to see the stars that remain there.
Kaminski said that, right now, the available evidence suggests that CK Vulpeculae is a red nova. But it’s possible that in 10 years, someone will come up with a different explanation for how this stellar explosion came to be.
“This is science and astronomy: You propose something new, and everyone is welcome to find supporting evidence, or disprove it with some new theory or new observations,” he said.
This finding, which was made by the SOFIA flying observatory, may shed light on how the dust that helped form countless stars and galaxies was created, the scientists added.
The elements that make up everything from people to planets are essentially stardust. These elements are forged in stars by nuclear fusion, which fuse small atoms such as hydrogen and helium into larger ones such as carbon and iron. [Supernova Photos: Amazing Star Explosions]
For years, scientists have tried to explain the vast amounts of dust seen in the early universe. The leading explanation was that this dust was created by exploding stars known as supernovas.
However, researchers also thought supernovas should excel at shattering and destroying dust as well. Prior research suggested that up to 80 percent or more of the dust that supernovas might generate could get destroyed by the so-called “reverse shocks” of these explosions. Reverse shocks are shockwaves rebounding off the cold, dense matter surrounding supernovas.
“It’s been known that ‘we are all made of star stuff,’ but the details of how newly formed ‘star stuff’ survives to later become the seeds for stars and planets is a bit murky,” said lead study author Ryan Lau, an astronomer at Cornell University.
One potential alternative source of the ancient dust seen in the early universe was that “some less powerful stars that don’t go supernova go through a phase where they gently blow off their innards and form dust,” Lau said. “However, this way of forming dust isn’t very efficient, because it takes a while for these less powerful stars to evolve to that point.”
Now Lau and his colleagues have unexpectedly confirmed that supernovas can be dust factories.
“Finding this surviving dust is surprising to me because when I think of a supernova, I imagine a very harsh, violent environment that is very inhospitable to dust and other things that happen to be caught in the explosion,” Lau told Space.com.
The astronomers employed the Stratospheric Observatory for Infrared Astronomy (SOFIA), a joint project of NASA and the German Aerospace Center housed aboard a modified Boeing 747SP jumbo jet. They analyzed dust in the middle of Sgr A East, the remnant of a supernova located near the center of the Milky Way. This remnant, known as Sgr A East, is about 10,000 years old.
“We were on a flying observatory traveling at 600 mph (965 km/h) at an altitude of 45,000 feet (13,715 meters) to take images of a 10,000-year-old supernova remnant located 27,000 light-years away from us at the center of our galaxy,” Lau said. “No other currently operating observatory other than the Stratospheric Observatory for Infrared Astronomy could detect this dust.”
The scientists found that about 7 to 20 percent of the initial dust of the supernova survived its reverse shock.
“One of the most surprising things is that we were not expecting to see this at all,” Lau said. “We were looking at the two brighter features to the right and to the left of the supernova dust we found.”
The researchers suggest the dust survived the supernova’s reverse shock because of dense gas surrounding the explosion, which slowed the debris from the supernova, helping the dust cool greatly and preventing its destruction. This finding implies that ancient supernovas could have generated the vast amounts of dust seen in the early universe.
The scientists detailed their findings online today (March 19) in the journal Science.