Archive for the ‘exoplanets’ Category

Sun’s closest solo star may have company

November 14th, 2018
Diagram showing the location of nearby stars.

Enlarge / The position of Barnard's star relative to the Earth and its other neighbors. (credit: IEEC/Science-Wave/Guillem Ramisa)

From the phenomenal success of the Kepler mission and a proliferation of ground-based telescopes, we now know that planets are common in our galaxy. But the methods we've used to detect most of them are biased toward finding large planets that orbit close to their host stars. The farther a planet is, the less its gravity pulls at the star and the less light it blocks out when it passes between that star and Earth. Meanwhile, the focus has shifted to nearby stars, as astronomers have started building a catalog of targets for the next generation of telescopes.

These issues provide an intriguing backdrop for today's announcement that one of the closest stars to Earth has a super-Earth companion. Barnard's star is a red dwarf that is only six light years from our Solar System; only the three stars of the Centauri system are closer. But the new planet orbits far enough from Barnard's star that it had been missed by earlier attempts. The detailed follow-up that spotted it also hints at the possibility of a separate, more distant planet, and both could help inform our models of planet formation.

A new look

Barnard's star has been observed extensively over the years, partly because it's so close, partly because it's a prototypic example of a red dwarf star. These observations have included exoplanet searches, but nothing about the system stood out. But unless you observe a star regularly, there's a chance you won't happen to be looking at critical points in the planet's orbit.

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Europa’s future: A runaway greenhouse

August 1st, 2017

Enlarge (credit: NASA)

Stars like the Sun brighten over the course of their history, a trend that has significant consequences for the habitability of Earth and other bodies both in our Solar System and beyond. An icy world on the far edge of the habitable zone may turn into a temperate paradise given enough time.

Or, it could go straight to being a Venus-style hell if a new study turns out to be right. The study’s authors tuned a full-planet climate model loose on a planet covered in ice. The find that, under a level of incoming light that’s sufficient to melt the ice, the planet reaches a greenhouse state that would cause it to lose all its water to space and possibly head straight into a runaway greenhouse.

The only thing that saved Earth from a runaway greenhouse is, ironically, the presence of greenhouse gasses in its atmosphere.

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Kepler data may hold a Neptune-sized surprise, our first exomoon

July 31st, 2017

Enlarge (credit: NASA/JPL-Caltech)

One of the most important things we’ve learned from the Kepler mission is that, in many ways, our Solar System isn’t unique. Lots of stars have planets, many have multiple planets, and the list of planets includes many with sizes and densities similar to our eight planets. But there are lots of details of our own planets, like the composition and presence of atmospheres, that are much harder to examine at these distances.

One of the features we haven’t gotten a grip on is the presence of moons. Most of our Solar System’s planets have them, and they seem to form by a variety of mechanisms. We’d expect them to be common in exosolar systems, too, but so far we haven’t yet spotted any.

A new paper, which goes into extensive detail about the calculations needed to look for an exomoon, makes it clear why: we simply don’t have enough observation time to pick one up in most cases. But the paper also suggests there may be an exception, as the data hints at a Neptune-sized exomoon, though the statistics aren’t yet conclusive.

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