Many Earth-sized planets out there…

A new NASA survey indicates that Earth-sized planets are now thought to be common in the galaxy, and thus, probably the universe. As many as one in four stars similar to the sun could have Earth-sized planets orbiting them.


Credit: NASA/JPL & Caltech/UC Berkeley

From the press release:

Nearly one in four stars similar to the sun may host planets as small as Earth, according to a new study funded by NASA and the University of California.

The study is the most extensive and sensitive planetary census of its kind. Astronomers used the W.M. Keck Observatory in Hawaii for five years to search 166 sun-like stars near our solar system for planets of various sizes, ranging from three to 1,000 times the mass of Earth.

All of the planets in the study orbit close to their stars. The results show more small planets than large ones, indicating small planets are more prevalent in our Milky Way galaxy.

“We studied planets of many masses — like counting boulders, rocks and pebbles in a canyon — and found more rocks than boulders, and more pebbles than rocks. Our ground-based technology can’t see the grains of sand, the Earth-size planets, but we can estimate their numbers,” said Andrew Howard of the University of California, Berkeley, lead author of the study. “Earth-size planets in our galaxy are like grains of sand sprinkled on a beach — they are everywhere,” Howard said.

The study is in the Oct. 29 issue of the journal Science.”

See also the University of California press release. These findings would appear to confirm the preliminary findings from the Kepler space telescope as well, in that smaller rocky worlds are more common than larger gas giants, which bodes well in the search for life.

Weird warm spot on an exoplanet

As more exoplanets are found on virtually a weekly basis, it is becoming apparent how diverse they are, sometimes with peculiar characteristics not seen before. Such is the case with the large “hot Jupiter” planet upsilon Andromedae b, which orbits very close to its star and so is searingly hot on the side facing the star (it keeps the same side toward the star, as the moon does as it orbits the Earth). Well, not quite. For some reason, the “hot spot” with the highest temperature is about 80 degrees away, almost on the other side of the planet.


Credit: NASA/JPL/Caltech

The observations were made using the Spitzer Space Telescope, and astronomers don’t have an explanation yet, but theories include supersonic winds and star-planet magnetic interactions.

Two steps closer to finding another Earth

This past week, there were two more news items of great interest relating to exoplanets, and the search ultimately for another Earth-like planet.

The first, from the Kepler mission, is that the previously reported possible planet Kepler 9d, only 1.5 times larger than Earth, is likely to soon be announced as confirmed. Other news from the mission will also be announced in November according to the same update.

Artist's conception. Credit: Lynette Cook

Then, another very significant announcement from ground-based observatories at the University of California Santa Cruz, the University of Hawaiʻi at Mānoa and the Carnegie Institution of Washington, that for the first time, a small rocky planet has been confirmed orbiting well within the “habitable zone” of a nearby star, the region where temperatures would allow liquid water to exist on a planet; not too hot and not too cold. One of six known planets orbiting the red dwarf star Gliese 581, about 20 light years away, it is estimated to have a mass about three times that of Earth, and a diameter of only about 1.2 to 1.4 times that of Earth. Additional reports here, here and here. A good quote from the UCSC article indicates how planets like this are probably quite common:

The researchers also explored the implications of this discovery with respect to the number of stars that are likely to have at least one potentially habitable planet. Given the relatively small number of stars that have been carefully monitored by planet hunters, this discovery has come surprisingly soon.

“If these are rare, we shouldn’t have found one so quickly and so nearby,” Vogt said. “The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy.”

This also brings the total count of known exoplanets so far to 492 and we’ve still only scratched the surface…

The case of the missing methane

In our solar system, all of the gas giant planets have abundant methane in their atmospheres. It was expected that similar planets in other solar systems would also, but one has been found which doesn’t… the planet GJ 436b, about the size of Neptune, orbiting a star 33 light-years from Earth. Based on analysis by the Spitzer Space Telescope, it appears to have almost none, which is a mystery. It should be noted that methane on these types of planets is primordial methane, a very simple molecule, left over from the planets’ original creation. On small rocky planets like Earth and Mars (and it exists on both), it can be either geological or biological in origin. In the case of Mars, the origin is still uncertain.

Artist's conception. Credit: NASA/JPL-Caltech
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