There are at least as many planets in the galaxy as there are stars. And even that is probably a vast underestimate.

That’s the latest bombshell from astronomers looking for planets beyond our solar system. Phil Plait at Bad Astronomy will have a post on this soon, but for now, here’s a little quote salad for you:

“Planets are like bunnies; you don’t just get one, you get a bunch,” said Seth Shostak, a senior astronomer at the SETI Institute who was not involved in this research. “So really, the number of planets in the Milky Way is probably like five or 10 times the number of stars. That’s something like a trillion planets.” (via PopSci)

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What’s the News: Using data from NASA’s Kepler spacecraft, astronomers from Princeton University and the Harvard-Smithsonian Center for Astrophysics have discovered the darkest known planet. The exoplanet, called TrES-2b, is located about 750 light-years away from Earth and reflects less than 1 percent of the incident light from its parent star, making it blacker than the blackest piece of coal. The discovery was published recently in the Monthly Notices of the Royal Astronomical Society (pdf).

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What’s the News: While the Kepler spacecraft is busy finding solar system-loads of new planets, other astronomers are expanding our idea where planets could potentially be found. One astronomer wants to look for habitable planets around white dwarfs, arguing that any water-bearing exoplanets orbiting these tiny, dim stars would be much easier to find than those around main-sequence stars like our Sun. Another team dispenses with stars altogether and speculates that dark matter explosions inside a planet could hypothetically make it warm enough to be habitable, even without a star. “This is a fascinating, and highly original idea,” MIT exoplanet expert Sara Seager told Wired, referring to the dark matter hypothesis. “Original ideas are becoming more and more rare in exoplanet theory.”

How the Heck:

• Because white dwarfs are much smaller than our Sun, an Earth-sized planet that crossed in front of it would block more of its light, which should make these planets easier to spot. So astronomer Eric Agol suggests survey the 20,000 white dwarfs closest to Earth with relatively meager 1-meter ground telescopes.
• And because white dwarfs are so cool, a planet in a white dwarfs habitable zone would be very close, meaning its transit would happen very fast. Agol says we’d only need to watch a star for 32 hours to pick up on any transiting, habitable planets.
• One leading theory about dark matter is that it’s made of theoretical particles called WIMPS (weakly interacting massive particles). It’s thought that when WIMPs collide (if, of course, they exist), they would explode. Astronomers think that these WIMP explosions could possibly heat a planet enough to make it habitable.
• There are no immediate plans to test the dark matter hypothesis, which is quite theoretical, and any plan to find dark matter-fueled planets would need to look far from here: our part of the universe doesn’t have nearly enough dark matter to bring a planet to habitability.

What’s the Context:

• In other white dwarf news, astronomers have discovered a red dwarf in an extremely tight orbit with a white dwarf.
• And others are still wrangling over what dark matter really is.
• As for exoplanets, astronomers have actually seen one—as in, with visible light—orbiting its star.

Not So Fast:

• It’s not at all clear if white dwarfs have any planets, and if so, whether any of them could possibly support water or life as we know it. For one thing, planets in the habitable zone would be tidally locked with the star—permanent scalding daylight on one side; permanent frozen nighttime on the other.
• Taking 32 hours to find a planet orbiting a white dwarf may seem like a short time, but when you’re looking at tens of thousands of stars, it adds up. Agol told UW Today, “This could take a huge amount of time, even with [a network of telescopes].”
• And just like star-orbiting planets have their Goldilocks zones (not to hot or too cold), dark matter-containing planets would need the right amount of dark matter to be habitable. “It’s not something that’s likely to produce a lot of habitable planets,” Fermilab researcher Dan Hooper told Wired. “But in very special places and in very special models, it could do the trick.” 

References: Eric Agol. “TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS.” doi: 10.1088/2041-8205/731/2/L31

Dan Hooper and Jason H. Steffen. “Dark Matter And The Habitability of Planets.” arXiv:1103.5086v1

Image: NASA/European Space Agency

What’s the News: Based on early Kepler data, astronomers say that the Milky Way galaxy may house at least two billion Earth-like planets—one for every several dozen sun-like stars. As NASA researcher Joseph Catanzarite told Space.com, “With that large a number, there’s a good chance life and maybe even intelligent life might exist on some of those planets. And that’s just our galaxy alone — there are 50 billion other galaxies.” But while 2 billion sounds like a lot, it’s actually far below many scientists’ expectation; Catanzarite says his teams’ findings actually show that Earth-like planets are “relatively scarce.”

How the Heck:

• Using mathematical models to plot the size and orbital distance for all the potential planets spotted during four months’ worth of Kepler data, astronomers extrapolated the data and calculated that 1.4 to 2.7% of the Milky Way’s sun-like stars may have an Earth analog.
• Two percent of the Milky Way’s roughly one hundred billion sun-like stars means that “you have two billion Earth analog planets in the galaxy,” Catanzarite told National Geographic.

What’s the Context:

• The Kepler team recently announced a mother lode of 1,200 potential alien worlds (68 of them about Earth size), a tightly scrunched-up mini solar system, and a bizarro “styrofoam” world; unfortunately, the “most Earth-like planet” planet it found so far got a major demotion: it’s not actually habitable.

Not So Fast:

• MIT astronomer Sara Seager says that the team “completely underestimates the frequency of Earths.” The calculations are based on only four months of Kepler data—too early to be making an accurate projection.
• There’s also the fact that Kepler can only detect the size and orbital distance (and occasionally the masses) of planets, which doesn’t tell you whether life as we know it could actually live there; Venus, for example, would roughly like Earth to aliens peering at us from many light-years away, but because of its atmosphere’s runaway greenhouse effect, it’s way too hot to be habitable.

Next Up: The astronomers plan on calculating an even more accurate number once all of Kepler’s data is in.

Reference: Joseph Catanzarite and Michael Shao. “The Occurrence Rate of Earth Analog Planets Orbiting Sunlike Stars.” arXiv:1103.1443v1 Image: Kepler/NASA

Last month, when astronomers with the Kepler space telescope released a list of 1,235 possible planets orbiting other stars, one particular candidate, KOI 326.01, especially stood out. Scientists, journalists, and the general public couldn’t help it: In a population of planetary candidates dominated by sizzling, Jupiter-sized gas giants—which are much easier to spot—here was the closest thing yet to our very own planet. It was just about the size of Earth, even a little smaller, and had a temperature around 138 degrees—rather warm for human tastes, but still a place where liquid water could rain down from clouds into oceans, and where life as we know it could possibly exist. A clever but perhaps overambitious monetary calculation valued the planet at exactly $223,099.93.

Alas, KOI 326.01’s 15 minutes of fame must now end. Additional analysis of the planet’s star now suggests that the planet is a lot larger, and most likely a lot hotter, than previously thought. “The details of the planet need to be hammered out, but this certainly means that this is not an Earth-size planet in the habitable zone,” where liquid water could exist, says Natalie Batalha, a Kepler team member.

The road to demotion began when a DISCOVER fact-checker, Mara Grunbaum, asked for some additional information about the planet. In response, Batalha and her colleagues dug up images of the sky near KOI 326.01—and almost immediately found a problem. The planet’s sun, known as KIC 9880467, is located close to another star (see above). In a reference catalog characterizing the stars in the probe’s field of view, KIC 9880467 is listed as brighter than its neighbor. But as you can easily see in the above image, that is not the case.

That simple error messes up the calculations of the planet’s temperature and size. Kepler finds planets by detecting tiny dips in a star’s brightness during transits—when a planet crosses in front of it. When the Kepler team analyzed the combined light from the two stars, they assumed KIC 9880467 accounted for most of the brightness. Now they have to chalk up almost all that light to the neighboring star. In fact, while Batalha is still confident KOI 326.01 exists, she is no longer sure which of the two nearby stars it is orbiting. In either case, the calculations indicate that the planet is somewhat warmer and a lot larger than the previous estimate. And if it is orbiting the bright, neighboring star, as Batalha suspects, the planet’s temperature will soar. More analysis is required, but it’s safe to say that KOI 326.01 should no longer be considered potentially habitable.

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Young. Old. Scalding hot. Icy cold. Terrestrial midgets. Gas giants. As the cavalcade of planets spotted beyond our solar system continues to grow, we get to see worlds of all sorts—and we get to speculate on the staggering number of exoplanets that might inhabit just our own galaxy.

Today’s first piece of otherworldly news involves baby exoplanets. Astronomer Christian Thalmann says his team may have spotted planets in the process of forming around three different stars, the first time scientists have spotted the process in action.

An infant star forms from a collapsing cloud of dust and gas and gathers a dense, flat disk of material that rotates with the star like a record album. The material in the disk will eventually clump up into nascent planets. Theoretical models of planet formation predicted that those protoplanets should suck up more gas and dust with their gravity, clearing a wide gap in the otherwise solid disk. [Wired]

Peering at young stars like T Chamaeleontis (T Cha) LkCa15 and AB Auriga, Thalmann and colleagues saw those telltale gaps in the dusty rings (their study is forthcoming in the Astrophysical Journal Letters). The stars are much like our own sun, so these pictures of infant solar systems could resemble what our own looked like as a baby. But though the stars are nearby in cosmic terms—T Cha lies just 350 light years away—the gaps are faint enough that it’s difficult to tell for certain if newly forming planets, and not the influence of binary stars or other objects, are creating them.

If Thalmann’s team is right, catching the birth of new worlds would be a great scientific coup. Our galaxy, however, isn’t exactly hurting for planets.

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For months we here at DISCOVER have been waiting impatiently for the Kepler mission to open up its vault of new exoplanets, hopefully filled with a bevy of Earth-like worlds and other exotic planets. Today planet lovers got a new peek at the Kepler findings, and those findings are stunning.

First, the Kepler scientists announced more than 1,200 candidate planets, which got DISCOVER blogger Phil Plait excited:

This is incredible! Even though I was expecting a number like this, actually hearing it for real is stunning. In 15 years we’ve found about 500 planets orbiting other stars, but in the almost two years since Kepler launched it may have easily tripled that number! Now, to be careful: these are candidate planets, which means they have not been confirmed. But in most cases these look pretty good, and if these numbers hold up it indicates that our galaxy is lousy with planets. They’re everywhere.

While those 1,200 are candidates, astronomers have confirmed a peculiar and fascinating set of six. From Phil Plait:

Using NASA’s orbiting Kepler observatory, astronomers have found a complete solar system of six planets orbiting a sun-like star… and it’s really weird: five of the six planets huddle closer to their star than Mercury does to the Sun!

None of them is what I would call precisely earth-like — they’re all more massive and much hotter than Earth — but their properties are intriguing, and promise that more wonderful discoveries from Kepler are coming.

Related Content:
80beats: Astronomers Predict a Bonanza of Earth-Sized Exoplanets
80beats: How Excited Should We Be About the New “Goldilocks” Exoplanet?
80beats: Astronomers Find a Bevy of Exoplanets; Won’t Discuss Most Interesting Ones
DISCOVER: How Long Until We Find a Second Earth?

ESO/L. Calçada

The Kepler space telescope, launched nearly two years ago, has already proven its worth as an exoplanet hunter many times over. But the discoveries keep on coming. NASA just announced that Kepler has found its first rocky planet–and that the rocky world is only 1.4 times the size of Earth, making it the smallest exoplanet ever found.

Phil Plait explains that this nearly Earth-sized isn’t actually Earth-like and habitable:

[I]t orbits extremely close in to its star, circling over the star’s surface at a distance of roughly 3 million kilometers (1.8 million miles) — amazingly, it takes less than an Earth day to make one circuit. But being that close to a star comes at a price: the surface temperature of the planet must be several thousand degrees!

The planet, Kepler-10b, may not be habitable to life as we know it, but Plait is still plenty excited. Get the rest of the story on how the planet was found and what its discovery means over at Bad Astronomy.

Related Content:
80beats: Astronomers Predict a Bonanza of Earth-Sized Exoplanets
80beats: How Excited Should We Be About the New “Goldilocks” Exoplanet?
80beats: Astronomers Find a Bevy of Exoplanets; Won’t Discuss Most Interesting Ones
80beats: After a Flawless Launch, Kepler Telescope Gets Ready for Planet Hunting
DISCOVER: How Long Until We Find a Second Earth?

The universe abounds with Earth-sized planets. That hopeful notion has been reinforced by individual planets finds like possible Goldilocks planet Gliese 581g, by the hordes of planet candidates discovered by the Kepler mission, and now, by a census of a small space in the sky that tells us one in four sun-like stars should possess worlds that are close to the size of Earth.

Take a moment to think about that: One in four.

In Science, exoplanet hunters Geoffrey Marcy and Andrew Howard published their team’s census of 166 nearby stars like ours, of which they picked 22 at random to investigate for planets. They watched the stars’ doppler shifts to hunt for planets over the last five years, and used the results to extrapolate how common terrestrial planets must be far beyond just this set of stars.

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The two newest planets spied by the Kepler space telescope are locked in a forever back-and-forth.

When Kepler’s scientists saw a star 2,000 light years away dim slightly, they knew there was the chance it was the telltale signature of a planet passing in front. But when the calculations were done and the confirmation came in, they found a surprise—what they’d seen was actually two planets transiting in front of the star.

NASA says it’s the first time they’ve ever caught such a sight, and today the scientists officially announced the finding with a study in Science. While other studies have found multiple planets around a single star–in fact, it happened earlier this week–those studies have used different planet-detection techniques like the wobble method.

The two worlds, both gas giants, do more than orbit the same star on the same plane, though. They push and pull each other in a motion that keeps the two exoplanets close to arithmetic celestial perfection. Kepler-9B, the larger, orbits the star in 19.24 days on average, the astronomers saw. Kepler-9c, the smaller, completes a revolution in an average of 38.91 days. But every time the scientists checked, 9b’s orbit was getting 4 minutes longer, while 9c’s shrank by 39 minutes.

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In August 2006, Pluto received its official demotion to dwarf planet status, taking our solar system down to eight planets. In August 2010, exoplanet hunters say they’ve found a haul of new worlds around a single star; that alien solar system may have seven known planets, meaning the system could be more like our home system than any ever discovered. And one of those worlds could be the smallest exoplanet ever found, too.

The star these planets orbit is called HD 10180, and it lies 127 light years from here. Astronomers at the European Southern Observatory in Chile used a spectrograph called HARPS to track tiny variations in the starlight caused by the pull of the planets.

It found clear evidence for five giant planets similar in size to Uranus or Neptune in our own solar system. But there were also tantalising signs that two other planets are also present, one of which would be the smallest, or least-massive, yet found orbiting another star [Christian Science Monitor].

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Although some publications glossed over the uncertainty in announcing the first findings of the planet-hunting Kepler mission, researchers say the overall point remains true: Earth-like planets (meaning that they’re small and rocky, not that they have aliens writing blogs about science) are not only not rare–they’re the most common type of planet in our galaxy.

The first intimations of this news came out a few days ago in reports like the Daily Mail’s, which blared that NASA’s planet-hunting Kepler mission had found 140 new planets that were like the Earth in size, and that worlds like our own could dominate the Milky Way. That claim came after a presentation now available to view online by one of the scientists behind Kepler, Harvard’s Dimitar Sasselov.

But Sasselov and colleagues responded to Space.com, trying to quell some of the excitement–or at least hedge on the exact magnitude of the find:

“What Dimitar presented was ‘candidates,’” said David Koch, the mission’s deputy principal investigator at NASA’s Ames Research Center in Moffett Field, Calif. ”These have the apparent signature we are looking for, but then we must perform extensive follow-up observations to eliminate false positives, such as background eclipsing binaries. This requires substantial amounts of ground-based observing which is done primarily in the summer observing season” [Space.com]

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We know about exoplanet HD 209458b, nicknamed “Osiris.” We know it’s 153 light years away, that it has water in its atmosphere, and that it orbits its star in three and a half days at a distance 100 times closer than Jupiter is to the sun. But we didn’t know this for sure until now: This planet has a tail.

In a study in The Astrophysical Journal, a research team says Osiris, a gas giant, orbits so close that its star is blasting away its atmosphere. As the planet progresses on its blazing hot and hasty revolutions, a tail like that of a comet follows behind it. The Hubble Space Telescope‘s Cosmic Origins Spectrograph caught the effect as Osiris made repeated transits in front of its star.

The instrument detected the heavy elements carbon and silicon in the planet’s super-hot 2,000 degrees F (1,100 C or so) atmosphere. This detection revealed the parent star is heating the entire atmosphere, dredging up the heavier elements and allowing them to escape the planet.

Jeffrey Linsky, of the University of Colorado, who led the study, said: “We have measured gas coming off the planet at specific speeds, some coming toward Earth. The most likely interpretation is that we have measured the velocity of material in a tail” [Christian Science Monitor].

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It’s the 1840s. Rival astronomers in Britain and France separately toil away in their notebooks, fiercely guarding their calculations of just where a planet beyond Uranus might be hiding, hoping that they and their country will get the glory for finding it. When telescopes finally spot Neptune, the discovery leads to decades of debate over primacy, and scouring each man’s private data to determine who deserved the most credit.

Fast forward to the 21st century: Rivalries may have changed, but in the hunt for new planets—especially becoming the first to detect a new world like our own in a distant star system—defending one’s data to lay claim to discovery has not gone away.

This week the team behind NASA‘s planet-hunting space telescope, Kepler, announced that it has found more than 700 new candidates for exoplanets. Given that the current tally of known planets beyond our solar system stands near 460, that’s a huge announcement. But what’s drawn some attention is that more than half of the candidates won’t be released publicly at this time. These include smallest planet candidates—those closest to our own world in size—which won’t be officially announced until February 2011.

It’s no secret why:

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NASA’s new eye in the sky has spotted the first handful of what it hopes will be a flood of new exoplanets. The Kepler telescope, launched last year with the express purpose of planet-hunting, has found its first five new worlds, with the results forthcoming in the journal Science this week. Just don’t get any ideas about living on any of them.

“One of the planets is amazingly light – like Styrofoam,” said William J. Borucki, the astronomer from NASA’s Ames Research Center…. “And all five simply glow,” he said, “they’re like looking into a blast furnace – but that’s simply no place to look for life” [San Francisco Chronicle]. The scalding-hot planets measure in excess of 2,000 degrees Fahrenheit, hotter than molten lava. These planets all orbit their stars in a hurry, taking between three and five days to make a circuit. Ground measurements confirmed Kepler’s findings.

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