[NOTE: I have been informed that this is NOT the first planet seen in the habitable zone of another star, but the first seen by Kepler, and moreover the first that is not a gas giant. Rather than try to correct the text below using strikethroughs, which would be confusing, I simply edited the text. I hope that's clear!]
This is pretty big news: the space-based Kepler observatory has confirmed it has found its first planet in the habitable zone of a star like the Sun! Not only that, the planet may well be similar to Earth, though that’s not clear yet.
The planet, called Kepler-22b, is about 600 light years away. The star it orbits, called simply Kepler-22, is a bit lower mass and cooler than the Sun. The planet takes about 290 days to circle the star once, and as soon as I saw that number I let out a little "yip" of surprise — that number’s perfect! Why?
Because that puts the planet inside of that star’s habitable zone, the distance where, given certain planetary conditions, liquid water can exist. It may be that life can arise where there’s no water, but we know life on Earth needs water, so if we’re looking for habitable planets it makes sense to look for the possibility of water there.
The planet is closer to its star than Earth is to the Sun — that’s why its year is shorter — but the star is cooler, compensating for that. That makes this the best candidate yet for Earth-like conditions. But is the planet like our own world?
Two new planets orbiting other stars have recently been discovered using NASA’s orbiting Kepler telescope. And while every new planet discovery is pretty amazing, normally two more add to the hundreds already confirmed wouldn’t really be newsworthy. However, these two weren’t discovered by professional astronomers! They were found by members of the Planet Hunters "citizen scientists" team; regular folks who have volunteered to sift through data returned by the observatory in hopes of finding far-flung worlds.
One of the planets found orbits its star with a period of just under 10 days, and the other orbits a second star in just under 50 days. Both are much more massive than Earth; the first is 2.65 times and the second over 8 times our diameter. The relatively lower mass means the first one might be rocky (as opposed to a gas giant) but the short period means it’s hot, far hotter than Earth.
Both planets transit their stars as seen from Earth. In other words, they pass directly in front of their stars from our point of view, blocking the light a wee bit. This drop can be measured, and the planet detected. By knowing how big the star is (a dwarf, a giant, whatever) the period of the planet can be found, and the size of the planet can be determined by how much light is blocked, too.
The Kepler observatory is staring at about 100,000 stars all the time to look for these mini-eclipses, and astronomers use a fleet of software to automatically tag suspicious changes in starlight. But it’s pretty hard to look through all the potential planet data, and that’s why Planet Hunters was set up: let people go through the data themselves, using their keen eyes and powerful brains to look for anything that might be a planet.
And it worked! The two planets discovered were just announced in a paper led by the Kepler team (PDF). Here’s a plot showing one of the transits:
On Sunday I posted about NASA’s twin STEREO spacecraft, which are now 90° ahead and behind the Earth in its orbit. From their vantage point, over 200 million kilometers away, they can together see the entire far side of the Sun and beam the images back to Earth, providing us with real time data impossible to get from home.
While I was going through old blog posts to look at entries I had written about STEREO, I found one showing some STEREO data that I thought was worth showing everyone again. Putting it in Sunday’s article would’ve made it too long, so here it is on its own.
Let me interject a personal note first. I was at NASA’s Goddard Space Flight Center working on Hubble when STEREO was first being put together as a mission. I remember thinking how cool it would be to see the entire Sun at the same time, and what it would mean to my friends over at the heliospheric physics section. I have a decent imagination, but still there was no way I could’ve ever foreseen some of the things STEREO has brought us — Nature is always more clever than any one of us. And my favorite of all of them, sent back while the two spacecraft were still relatively near the Earth, is this incredible animation showing something that can never be seen from Earth: the tiny disk of the Moon transiting the Sun:
From Earth, that would be a solar eclipse, where the black disk of the Moon would look the same size as the bright Sun. But from well over a million kilometers away — the distance STEREO B was when it took these images — the Moon is smaller, providing this eerie and beautiful view that is a stunning reminder that humans are a spacefaring species, and the views we get from there expand our world.
Wow! You can see the Sun’s rotation over the four hour interval these pictures were taken, and then the Moon flashes by. The Moon is dark because it’s between us and the Sun, so were seeing the unlit side (I have a diagram showing an approximation of the geometry of this event on my other page about it).
Moreover, scientists can use images of the sharp-edged Moon against the Sun’s disk to check on the optics of the observatory. That information can be used to sharpen the images even more. So this is fantastic, fantastically beautiful, and fantastically useful, too.
For their Picture of the Week last, uh, week, the Solar Dynamics Observatory crew chose a fantastically cool shot: the Moon cutting across the disk of the Sun!
Wow! This phenomenal shot was taken on October 7, 2010, as the new Moon slipped between the Sun and the observatory. SDO is in Earth orbit, circling our planet 36,000 km (22,000 miles) up (technically, that’s the distance from the Earth’s center). The orbit is tilted so the Earth itself only rarely gets in the observatory’s way as it watches the Sun day in and day out.
But every now again, when the celestial objects literally align, the Moon can block the view. From the Earth, the Moon was new, meaning it was near the Sun but not blocking it. But from SDO’s point of view the geometry was just right to get this partial eclipse (technically called a transit). I drew a rough diagram to give you an idea of how this worked:
The European Southern Observatory has unveiled a new planet-hunter: TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope. I know, I know, but we’re running out of acronyms here, folks. If it makes you feel better, it was named after a beer.
In the meantime, it also takes incredible pictures of the sky:
That’s the Tarantula Nebula, a sprawling complex of gas and dust churning out stars at an incredible rate. To give you an idea of how luminous it is, at 180,000 light years away (that’s 1.8 quintillion kilometers, or more than a quintillion miles!) it’s still visible to the naked eye (if you live in the southern hemisphere, that is). TRAPPIST’s primary mission is to look for transiting planets as well as comets visible in the southern skies, but like any good telescope pointing up it’s capable of all sorts of good science — if, for example, there are any changes in the Tarantula (a star explodes, or flares up) TRAPPIST will catch it. (more…)
That’s an artist’s illustration of one of these planets. As you can see in the diagram, the star rotates left-to-right, but the planet orbits right-to-left. That’s a bit of a puzzler, and here’s why. (more…)
Phil Plait, the creator of Bad Astronomy, is an astronomer, lecturer, and author. After ten years working on Hubble Space Telescope and six more working on astronomy education, he struck out on his own as a writer. He's written two books, dozens of magazine articles, and 12 bazillion blog articles. He is a skeptic and fights the abuse of science, but his true love is praising the wonders of real science.
The original BA site (with the Moon Hoax debunking, movie reviews, and all that) can be found here.
Contact me: The Bad Astronomer "at" gmail "dot" com
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This is pretty big news: the space-based Kepler observatory has confirmed it has found its first planet in the habitable zone of a star like the Sun! Not only that, the planet may well be similar to Earth, though that’s not clear yet. 
