As we find more and more planets orbiting other stars, we keep finding ones that are weirder and weirder. Enter GJ 1214b: while much more massive than the Earth, it’s apparently mostly water!
[Click to enhydronate this artists's illustration.]
The planet — orbiting the star GJ 1214 at 40 light years from Earth — was actually discovered in 2009 by the MEarth project, which is looking for Earth-like planets around, cool, dim red dwarf stars. This is fertile ground for the search: these stars are extremely common, making up something like 80% of the stars in the sky. Not only that, but because they are cool, a planet at the right temperature to have liquid water on the surface would have to be close to the star. That means its period is shorter, making it easier to find (you don’t have to wait a long time for the effects of its orbit on the star to be seen).
In this case, though, it’s not terribly Earthy! First off, it’s massive, weighing in at
2.7 6.5 times our own planet’s mass. It’s also orbiting the star at a distance of a mere 2 million kilometers, giving it a temperature of something like 230° Celsius (450° F): hot enough to roast a chicken.
But it apparently has something the Earth does: water, and lots of it. From our viewpoint, the planet passes directly in front of its star once every 38 hour orbit (this is called a transit). When it does, it blocks the star’s light a little bit (which is how it was discovered). But the planet also has a thick atmosphere, and when it passes in front of the star, that atmosphere absorbs some of the starlight. As it happens, different things in the atmosphere absorb light differently. Water vapor, for example, has a different impact on a spectrum taken of the star’s light than, say, carbon dioxide.
So by breaking the light up into lots of colors and carefully measuring it, it’s possible to figure out what’s in the planet’s atmosphere. Earlier observations could tell that something was absorbing starlight, but they couldn’t tell what. New Hubble observations (PDF) indicate that the best fit to the observations is: water. Haze, for example, absorbs more visible light than infrared, but that’s not what was seen. The spectrum matches the way water absorbs light best, and in fact indicates the atmosphere may be as much as 50% water by mass!
Given the planet’s size of about 35,000 km (22,000 miles), its density is quite low: about 2 grams per cubic centimeter. Compare that to Earth’s density of 5.5 grams per cc! A rocky world more massive than Earth would most likely be denser than 2 grams/cc, so that’s consistent with this planet having lots of water (which has a density of 1 gram/cc).
The scientists involved indicate this planet would be really weird. There may be exotic forms of water there, due to the high temperatures and pressure deep in the planet’s atmosphere. Most likely the planet formed farther out from the star and migrated inward, a phenomenon that is apparently very common in planetary systems. I’ll note other planets like this have been found, too, but not with such a high-precision spectrum and therefore such certainty.
I know that our solar system is pretty weird; we have all manners of strange things floating around in it. But there’s nothing like seeing something so weird it makes us look positively normal by comparison. Sometimes we really do need a swift kick in the planets.
[P.S. My hearty congrats to Zach Berta, the lead author on the Hubble observations. I got to interview him for an Episode 2 of "Bad Universe", and he was very welcoming and fun to hang out with (and got an IMDB credit out of it). We talked quite a bit about GJ 1214b for the interview, and I'm glad to see this planet and its discoverer get some press!]
Image credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)
- Exoplanet in a triple star system smack dab in the habitable zone
- Motherlode of potential planets found: more than 1200 alien worlds!
- Another Kepler milestone: Astronomers find two Earth-sized planets orbiting the same star!
- Super Venus steampunk planet!
There’s cold water vapor orbiting the star TW Hydrae… and a lot of it. Enough to fill the Earth’s oceans thousands of times over!
TW Hydrae is a star located pretty close by, about 175 light years away. It’s lower mass than the Sun, so it glows an orange-red, but it’s also very young, less than 10 million years old. Stars that age are still shaking off the remnants of their formation, and that’s just the time you expect planets to get started.
And in fact it’s been known for years that TW Hydrae is surrounded by a giant disk, the leftover materials from its formation. Disks like that around other stars have been closely scrutinized, and we see lots of different materials in these disks, including various minerals, complex dust molecules, and even water. In general the water that’s been found is usually close in to the star and warm (which makes it easier to see).
Astronomers used the orbiting Herschel telescope to look at the disk of the star TW Hydrae in the infrared, and found water in the spectrum of the material there. And what they discovered is that it’s cold vapor, not warm. That’s the first time this has even been seen, and it’s kinda neat how this was done.
For the past few years, tantalizing evidence has been found that Mars — thought to be long dead, dry, and lifeless — may have pockets of water just beneath the surface. To be clear, we know there’s water on Mars, in the form of ice. We see ice in the polar caps, and we’ve seen it revealed under the surface by small meteorite impacts.
The question is, is there liquid water?
New images by the Mars Reconnaissance Orbiter bring us a step closer to answering that question. A series of pictures of the 300 km (180 mile) wide Newton crater taken over the course of several years show dark deposits on the crater wall which change predictably with the seasons, clearly affiliated with some sort of material flowing downslope:
[Click to barsoomenate.]
The picture above shows Newton’s crater wall. It’s pretty steep, with about a 35° slope, and the dark deposits are labeled. This crater is located in the southern mid-latitudes of Mars, and this part of the crater faces north. That’s critical! Since it faces toward the equator, that means it’s facing the Sun in the summer, and so these deposits appear when the temperatures get warm.
NASA has created several animated gifs (too big to embed here) that show the growth and retreat of these features over time. You can easily see how these dark features change.
In the past, similar things have been seen in gullies on Mars. It’s not clear those are from water, since frozen carbon dioxide can also be thawing out and forming them. In those cases, the flows were seen on the cold-facing sides of crater walls, making it less likely they’re from water. These new formations are on the warm-facing side, making it more likely they are from water.
So what’s going on? Read More
Like any scientist, I love a good mystery. Sometimes it’s fun when they are long, complicated, involve subtle and difficult layers, and require a vast effort to unravel.
And sometimes it’s cool when they are simply stated and simply solved. Like asking "Where does the water in Saturn’s upper atmosphere come from?" and finding out the answer is "It rains down from the moon Enceladus."
Water has been seen deep in Saturn’s atmosphere before, but a few years back it was detected in the upper atmosphere as well, and that’s a bit weird; there don’t appear to be any ways to get it from deep down in Saturn to the top parts of its clouds. So how did it get there?
Well, the tiny, icy moon Enceladus was discovered to have geysers at its south pole, actively spewing out quite a bit of water into space. Most of it goes into space and is gone forever. Some actually forms a ring around Saturn called the E-ring, and some no doubt hits other moons. Generally, when a moon blasts stuff into space (like Jupiter’s moon Io does with its sulfur volcanoes) the material forms a big donut-shaped region around the planet. It was figured that Enceladus was doing the same thing with water around Saturn, but even the Cassini spacecraft, which is right there, couldn’t detect it. It’s pretty hard to sample.
But astronomers used Herschel, an Earth-orbiting infrared observatory, to observe Saturn. They found a peculiar feature in the infrared spectrum of Saturn, and realized it’s from this Enceladusian water torus. Apparently, about 3-5% of the water from Enceladus’s geysers falls on Saturn, literally raining down in sufficient quantities to explain the presence of the water detected in the ringed planet’s upper atmosphere.
Scientists studying samples of volcanic glass from the Moon have made a startling discovery: there’s more water in them than was once thought. A lot more water. Not enough to go swimming or anything like that, but certainly enough to have affected the Moon’s geologic history, and potentially profoundly impact (haha — see below) our ideas of how the Moon formed.
The scientists looked at glass created in volcanic fire fountains, eruptions billions of years ago that left tiny (roughly the diameter of a human hair) grains of colored glass on the surface. These lay there for quite some time until 1972, when they were spotted by geologist Harrison Schmitt, who happened to be standing on the Moon at the time as part of Apollo 17. He brought them back to Earth for study.
In the ensuing decades technology improved quite a bit, and figuring out the contents of the glass beads has become a lot more accurate. In this new research, the scientists found (in 2008, actually, but their results are now confirmed) that the beads have a water content of about 750 parts per million, roughly equivalent to what you’d find in magma in the Earth’s upper mantle. That’s very surprising; many of the rocks on the Moon’s surface are very dry*, which for years has led scientists to assume the Moon itself was very dry.
Even with subsurface water being found all over the Moon, it’s still surprising to see this water in the beads. Why?
The comet Hartley 2 has come and gone, and the NASA mission EPOXI is also moving on after an exceedingly close flyby of the comet’s solid nucleus. The pictures we got were fantastic and beautiful… but their real power comes from coupling them with spectra.
In the picture above — an enhanced version of one of the images taken during the space probe’s flyby — you can see fan-like emission coming from the comet’s nucleus. These are jets; sprays of material coming out of the nucleus. Comets are made of rock and ice, and when the comet nears the Sun, the heat can turn that ice directly from a solid to a gas. This gas then shoots out from pockets on the nucleus, creating these jets. The EPOXI team (including my old boss, Don Lindler!) made a fantastic animation from a series of observations showing these jets in action.
But what are these ices made of? Lots of things we normally think of as liquids or gas (water, ammonia, carbon dioxide, and so on) exist in comets. In many comets, we see lots of water, and in fact the Swedish satellite Odin detected about 200 kg/sec (440 pounds per sec) of water coming off Hartley 2! So is water powering these jets?
We can find out… using spectra. By breaking up the light from an object into its component colors, we can learn all manners of things including what it’s made of. EPOXI did just that with the jets streaming from Hartley 2, and while it did find water, amazingly, it found a lot more carbon dioxide!
Does liquid water still flow on Mars?
We know that in the distant past — like, a billion years ago — liquid water was abundant on Mars. We also know that water currently exists on Mars in the form of ice, sometimes just below the surface (where even small meteor impacts can reveal it). But can there still be liquid water flowing on Mars, even if only for a very, very short time?
Maybe. Just maybe.
On October 9, the LCROSS spacecraft watched as a Centaur rocket booster slammed into the south pole of the Moon, hoping to determine if any water ice exists under the lunar surface. The idea is that over millions of years, comet impacts and other events have brought water to the Moon. Most of it goes away over time, but if any water happens to accumulate at the bottoms of craters at the poles, where the Sun never shines, it can stay put, frozen forever in shadow. By impacting a spacecraft into the Moon, it can eject the ice where it gets hit by raw sunlight. The water breaks down into hydrogen and hydroxyl molecules (OH-), which can be directly detected.
The target crater, Cabeus, has a temperature on its floor of -230 Celsius, cold enough to store ice. The Centaur slammed into it at high speed, making a new crater about 20 meters across and splashing debris over an even bigger area. A plume went up and out of the crater, and it was that tower of ejected material that had the telltale signs of water. The infrared spectrometer on LCROSS definitely detected absorption lines from water, and the ultraviolet spectrometer saw it in emission. Not only that, the emission got stronger with time, which clinches the deal! That’s exactly what you expect by a plume containing water.
The amount of water they found in the plume was a couple of hundred kilograms in total, but that indicates there is a lot more still lying on the surface. They don’t know how much exactly just yet; NASA wanted to release this news as soon as they were sure they had definite results, but there is still much to do. Where did this water come from? How long has it been there? How accessible is it to future astronauts? These questions and more will, hopefully, be answered in the coming weeks and months as the data are analyzed more thoroughly. So stay tuned. There’s lots more good news to come!
When NASA slammed the
700 kg (1500 pound) 2400 kg (5200 pound) Centaur rocket booster into the Moon on October 9, the hope was that it would make a plume visible from Earth. Terrestrials were disappointed, however, when none was seen.
However, a better view was to be had by LCROSS, the Lunar Crater Sensing and Observation spacecraft, which shepherded and closely followed the rocket booster, impacting itself just minutes later. From its much closer (and doomed) location it spotted both the plume and the flash of impact! Here’s the plume:
I’ll be honest with you, it’s not much to see. For some reason, the plume was not several kilometers high as hoped, but instead more like only one or maybe two (and, it seems, blocked from our Earthly view by the rim of a crater). In the above image, taken 15 seconds after the booster impact, the plume was 6-8 kilometers wide. The fact that it was not as bright as hoped is itself interesting, however! The actual plume brightness was at the low end of what was expected, which may be due to the nature of the material it slammed into.
There was never really a chance to see the flash from Earth, since it was at the bottom of a crater blocked from our view. But LCROSS was directly above the crater when the Centaur hit, and took several images, including the one shown here right at the moment of impact. This image shows the flash in the mid-infrared, beyond what our eyes can see but where a lot of the energy of the impact went. Other images can be found on the NASA site.
The crater carved out by the Centaur was less than 30 meters across. That’s far too small to be seen from Earth (our limit, even with Hubble, is more than 100 meters in size), but the orbiting Lunar Reconnaissance Orbiter should be able to see it easily, and in fact did take observations of the impact just a minute or so after it happened.
All of these data are being analyzed right now. Did any of those instruments see the signature of water in the plume?
Did the much larger LCROSS impact (it had a mass of 2000 kg) dig up any water? No one’s telling right now, but I suspect we’ll know soon enough. You can read more about this at Universe Today.
Update: Somehow, in my head, I got the masses of LCROSS and the Centaur reversed. Apologies, and thanks to IVAN3MAN for correcting me!