Exoplanets found nearby

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Worlds without end: Astronomers have identified three planets close to the habitable zone on a star only 39 light years away.

A year on the two inner planets lasts just a couple of days. Data on the third world are sparse; it could take anywhere between 4.5 and 72.8 days to trek around its sun. The star, designated 2MASS J23062928−0502285, is roughly the size of Jupiter — about one-tenth as wide as our sun — and about 3,200 degrees Celsius cooler than the sun. Such runts make up about 15 percent of the stars in the galaxy, though astronomers had not found planets around one before. All three planets were discovered as periodic dips in starlight in late 2015 using TRAPPIST, a telescope at La Silla Observatory in Chile.

If anything does crawl or grow on these worlds, it bathes in mostly infrared light. The innermost planets receive several times as much energy from their star as Earth does from our sun, which technically puts them outside the star’s habitable zone (SN: 4/30/16, p. 36). But the planets are huddled up so close to the star that gravity might keep them from spinning, creating a temperate zone along the line where day turns to night, the researchers suggest.



  • I’ve noticed that a seeming majority of exoplanets tend toward the extremes: temperature, gravity, spin, whatever. Are we only seeing what we can detect, or what is actually out there?

  • The first. Our sample is very biased at this point.

  • Edward

    Exoplanets are most easily found by seeing the effects of their orbits (e.g. Doppler changes to their stars or occultation, as with Kepler). Astronomers like to see two — or preferably three — orbits of these effects before suggesting that a planet exists to cause them, and since we have only been looking for two decades, Planets with orbital periods greater than seven to ten years have yet to be “discovered,” only suspected. Those with orbits of days or weeks are quickly discovered, so long as we are looking at their stars.

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