October 30, 2013
Scientists following up on data from the Kepler planet-hunting telescope have identified Earth’s closest twin yet—at least in terms of size and mass. Measuring only 1.2 times the radius of Earth, Kepler -78b is now the smallest planet for which we also know the mass: about 1.7 times Earth’s. The two planets have roughly the same density, which means Kepler-78b is probably made of rock and iron too.
That’s pretty much where the similarity ends, though. Kepler-78b orbits perilously close to its host star—so close, in fact, that its year lasts only 8.5 hours, and surface temperatures are several thousand degrees on the side facing the star. No water, no life, and no good explanation—at least not yet—for how such a small planet ended up so close to its star. According to current theory, the star would have been two to three times bigger than it is today when the planet formed. But if -78b started off in its current location, “the planet’s orbit would be inside the star itself,” which is clearly not possible, says Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics in Boston, speaking at a press conference today. One possible explanation is that the planet is the dead core of a gas giant planet that migrated inward from farther away, but that theory is problematic too, says Sasselov. He called -78b “a poster child for a totally new class of planets” that has recently emerged from the Kepler data.
The discovery sets a new standard for observing small, rocky worlds. Kepler found the planet and measured its radius last spring, but it wasn’t until the summer that two independent groups—one working with the HIRES spectrograph at the Keck Telescope in Hawaii and the other with the HARPS-N spectrograph at Italy’s Telescopio Nazionale Galileo in the Canary Islands—were able to make the exquisitely sensitive measurements that allowed them to calculate the mass of Kepler-78b, based on the spectral signature of the tiny planet tugging on the much bigger star.
The two teams reported their results in Nature magazine today.
October 18, 2013
A “rogue” exoplanet with the preliminary name PSO J318.5-22 has been detected by a group of astronomers led by Michael Liu from the University of Hawaii at Manoa. By “rogue planet,” astronomers mean one that has no host star – it wanders alone through galactic space.
This particular world is a Jupiter-type gas giant, located about 80 light years from Earth in a collection of young (less than 50 million years old) stars in the Beta Pictoris moving group. With only about six times the mass of Jupiter, PSO J318.5-22 is one of the least massive rogue planets detected so far. It’s a sub-brown dwarf, even less massive than a brown dwarf (a gas giant that failed to become a star).
Radiation levels within this type of planet are very high, with a seamless transition from gas to liquid in the deep atmosphere. Convection would move any organic compounds at the surface down into the interior, where they would encounter extreme temperatures and pressures. Thus, life within a gas giant like PSO J318.5-22 has to be considered extremely unlikely. But the rogue planet could be accompanied by a large moon, whose subsurface could be a potential abode of life.
The discovery gives credence to the notion that rogue planets might be very common. By some estimates, there could be as many as 100,000 of these nomads for each star in our galaxy!
According to current theories about solar system formation, small, rocky planets sometimes come close to very large planets in the chaotic early stages before their orbits stabilize. Such close encounters could potentially hurl the smaller planets out of the solar system entirely, leaving them to wander the galaxy as nomads. In fact, the Mars-size object that collided or had a near-collision with the early Earth (resulting in our unusually large Moon) is thought to have become a rogue planet.
Any planet bumped in this way from its original solar system might be very Earthlike, and life could already have taken hold. Once ejected, the atmosphere would freeze to the surface. However, heat from radioactivity in the core could provide enough energy to keep an ocean of water beneath the icy surface. And it’s distinctly possible that unicellular life and even subsurface life at hydrothermal vents could develop on this kind of “Steppenwolf planet.”
Under certain conditions, an ice layer might not even be necessary. A thick atmosphere of molecular hydrogen could provide enough pressure and insulation to keep liquid water on the surface, if the atmosphere had 100 to 10,000 times the pressure of Earth’s and the planet was ejected quickly. In that case, once again, the planet might retain primitive forms of life.
Thus, even if a planet loses its star, it doesn’t mean necessarily that it loses its inhabitants. Life can find many ways to persist.
February 23, 2012
Astronomers announced this week that they’ve confirmed the existence of a new class of planet — a hot, watery, exotic “super-Earth.”
A little over two years ago, astronomers at the Harvard-Smithsonian Center for Astrophysics discovered an exoplanet that we agreed was worth some extra attention. The planet, designated GJ 1214b, is only 2.7 times the diameter of Earth — one of the smallest exoplanets found — and orbits just over a million miles from its star (compare to Earth’s 92 million miles) in a zippy 38-hour ‘year.’
Given its size and density, astronomers speculated that GJ 1214b may very well be covered in deep oceans. The Harvard-Smithsonian team kept studying it, enlisting the Hubble Space Telescope to get more data about the planet’s atmosphere. “We’re using Hubble to measure the infrared color of sunset on this world,” said astronomer Zachory Berta in this week’s release. The data seem to confirm that GJ 1214b has a very steamy atmosphere, thick with water vapor.
Even more intriguing is that due to the temperature (being so close to its red dwarf star makes it around 450 degrees Fahrenheit) and extreme pressures, all that water gets a bit…exotic. Materials “like ‘hot ice’ or ‘superfluid water’ – substances that are completely alien to our everyday experience” would form, according to Berta. We emailed Berta to ask if he could explain these strange materials further.
Frankly, it’s difficult for me to imagine what these exotic forms of water would be like – we have very little experience with them here on Earth. They’re simply how the molecule H2O acts when it is in high pressure and temperature environments …
Our closest point of comparison is that the outer atmosphere might be something like a hot, steamy oven that you would use to bake bread with nice crust. But as you go deeper into the planet, you would encounter these exotic forms of water. I should add, however, that there’s still an enormous uncertainty about the composition of the planet overall. Yes, the observations point to a planet that is rich in water, but what is it mixed with, and in what proportions? Really visualizing the “surface” of this planet (if there is one!) will require us figuring those things out!
But whatever the case, the temperatures are too high for liquid water as we know it to exist on GJ1214b.
We feel obligated to point out that if you’re going to google “hot ice” like we did, the first hit you get is this video; we asked Berta if that’s what he was talking about. He replied, “Sadly, I don’t think the YouTube video would be a great example. It shows water that’s saturated with sodium acetate, and the sodium acetate is crystalizing into the solid form. I’d really rather you didn’t link to it [ed note -- Sorry!], because that’s not what we think is going on.” OK, we crossed it off our “What Hot Ice Might Be Like” list.
Given the existence of water, we also asked Berta if he would “speculate wildly” on the question of life on GJ 1214b:
There’s probably no liquid water anywhere on this planet, so nope, I won’t speculate wildly about what sort of life could live there. Sorry! I can’t imagine it – the temperature would be too high for the large, complex molecules that make life possible to survive. But I will say this, which I think is an important point along the same lines:
What makes me excited about these observations is really the technique, the idea that we can use a telescope to observe the atmosphere of a very distant planet. GJ1214b is too hot for life, but it’s not too difficult for us to imagine that we could make similar observations of the atmosphere of a planet that was a little cooler in temperature than GJ1214b and could potentially host life. Microbial and plant life on Earth have dramatically altered our atmosphere over its history. If they did the same on another planet orbiting another star, observations like these of that planet’s atmosphere might then be able to tell us whether or not there is life elsewhere in our galaxy.
February 2, 2011
When a veteran planet hunter like Debra Fischer calls it the most momentous discovery since 51 Peg, you know it must be big.
In 1995, scientists found the first planet circling a normal star outside our solar system—an unassuming yellow dwarf called 51 Pegasi. In the 16 years since, they’ve identified more than 500 such exoplanets.
Today they tripled the total in one announcement.
Actually, the Kepler spacecraft science team is only claiming 1,253 new candidate planets, based on four months of staring at 155,000 stars in the constellation Cygnus. Most still need verification with ground-based telescopes, and perhaps 20 percent of the claims will wash out, according to Fischer, who was on the panel presenting the Kepler findings to the press today.
Still, the number is impressive. According to Kepler project scientist William Borucki, his telescope is only surveying 1/400th of the sky. So by extrapolation, half a million new planets might be out there, easily detectable with a Kepler-style telescope, which watches for dips in light as a dark planet crosses in front of a bright star.
Kepler’s new batch of 1,253 candidates includes 68 Earth-size- planets, 288 “super-Earths” (twice as big as our own world), 662 the size of Neptune, and 165 the size of Jupiter. The telescope even found one sun-like star called Kepler-11 with six planets, a record.
A whopping 54 of the new candidates orbit in the so-called habitable zone of their star, where temperatures would theoretically be moderate enough for life to exist. And five of those 54 are Earth-size.
Finding a true Earth analog—a planet the size of our own, circling a star similar to the sun at roughly the same distance—requires three years of data. That’s how long it will take to get repeated crossings of the sun’s disk for orbits the size of Earth’s.
So, says Borucki, we’ll need patience to find a close match of our own planet around another star. But that doesn’t mean some of the 54 planets announced today, or even their moons, couldn’t harbor life of some kind.
Meanwhile, you can join in analyzing the Kepler data at the “Planet Hunters” site. So far, says Fischer, some 16,000 people around the world have participated in this nifty example of “citizen science.” They’ve already turned up hundreds of candidates, most of which are likely to overlap the list released today by the professionals.
December 1, 2010
Having already found more than 500 planets circling distant stars, scientists are getting better at understanding what they’re made of. A group led by Jacob Bean at the Harvard-Smithsonian Center for Astrophysics reports in this week’s Nature that they’ve analyzed the atmosphere of a planet only slightly larger than our own for the first time. And they may have found water —or rather, steam.
The planet, called GJ 1214b, has a radius about 2.6 times larger than Earth’s, and orbits a star located 40 light-years away in the direction of the constellation Ophiuchus. Scientists knew from previous observations that the planet must have an atmosphere, because its density is too low for an all-rocky planet. Theoretical models suggest three possibilities: A) a cloud-free hydrogen atmosphere, B) high clouds or haze obscuring a deeper hydrogen atmosphere, and C) an atmosphere made mostly of water vapor.
Bean and his colleagues used the 3.6-meter Very Large Telescope in Chile to analyze the spectrum of starlight filtering through the planet’s atmosphere. The data led them to rule out option A and favor option C, the steam world (although B is still a possibility). And future infrared observations should be able to distinguish between B and C.
Sadly, though, “the planet would not harbor any liquid water due to the high temperatures present throughout its atmosphere,” say the authors.
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