Archive for the ‘exoplanets’ Category

Inside-out dense iron planets probably the result of massive collision

February 5th, 2019
Inside-out dense iron planets probably the result of massive collision


How violent are the early histories of solar systems? Planets are built by the collisions of smaller bodies, so a certain amount of violence is probably unavoidable. Our own Earth-Moon system seems to have been formed by a smash-up of two planets, while Uranus seems to have been flipped on its side by a collision, and Mercury seems to have lost a lot of its material early in its history. Is this sort of history common as planets form?

Answering these questions requires a detailed understanding of the planets themselves, knowledge difficult to attain for any solar system but our own. But now, following up on observations made with the Kepler space telescope, researchers are suggesting they've found evidence of a smash-up in an exosolar system about 1,750 light years from Earth.

That's dense

Kepler-107 has a Sun-like star orbited by at least four planets. The planets are tightly packed around the star, with orbital periods ranging from three to 14 days. The lengths of the orbits of neighboring planets can be expressed as simple ratios of integers (5:2, 3:1, and so on). This creates what are called "resonant orbits," where the periodic alignment of the bodies helps stabilize and reinforce the orbits. Generally, this is thought to occur when planets that form farther from the star are migrating inward toward it; the resonances help balance things out and keep the planets from continuing on into the star.

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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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