Across the Universe: Myriad planets
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This column first ran in The Tablet in September 2012 One hundred thousand planets. That’s the census we can infer for just one corner of the Milky Way Galaxy being watched by the Kepler space telescope, according to results presented [August 2012] at the International Astronomical Union in Beijing. Watching each of 145,000 stars in a bit of the Milky Way about 10 degrees wide over many years (three and a half years, [as of that time]), Kepler is looking for faint dips in brightness occurring on a regular basis that can be attributed to the passage, a “transit”, of a planet in front of that star. So far some 2300 candidate planets have been identified. (Many stars have more than one candidate.) But in order for us to see such a blip, the planet’s orbit must be lined up almost exactly between the star and us; we’re missing any planets whose orbits are tilted above or below their star … Continue reading

Across the Universe: Super Earths
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This column first ran in The Tablet in August 2015 Half the planets in our solar system are relatively small, rocky, and found near our sun. The other half are all significantly bigger, covered in giant atmospheres, and orbit far away from the sun. Explaining this trend in size and orbits is simple. If the planets formed from a disk of gas and dust (we’ve actually observed such disks around young stars) then planets forming farther from the sun are colder. If they’re far enough from the sun that water in the gas freezes into ice, they’ll jump up in size — a gas cloud has twice as much water as rocky material to snowball into a planet. And once a planet reaches a critical size, it captures gas from the nebula to make a thick atmosphere. So, inner rocky planets stay small; but once the icy outer planets get big enough, they jump up to even larger sizes. The … Continue reading

Across the Universe: Me and My Shadows
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This column first appeared in The Tablet in April, 2009. Last week [April 2009], NASA’s Kepler space telescope sent back its first images of a star field in the constellation Cygnus. Launched in March [2009], Kepler has been slowly positioning itself far from Earth’s bright clouds; unlike most spacecraft, it’s not a man-made moon orbiting the Earth, but a man-mad asteroid following the Earth around the Sun, with a “year” a few weeks longer than Earth’s. Now, from the darkness of its orbit, it has aimed its telescopes at the Milky Way to look for traces of Earth-like planets. The plan is simple. For the next three years (six years, if all goes well) it will be watching the same star-filled region of the Milky Way, carefully measuring the brightness of every star in its field of view – some 100,000 of them – looking to see if any one of them periodically dims by a hundredth of a percent or less. … Continue reading

Across the Universe: New Worlds
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First published in The Tablet in June, 2007. In early 2007, a team lead by Stéphane Udry of the Geneva Observatory announced the discovery around the red dwarf star Gliese 581 of a planet that is only eight times the mass of Earth and about 50 per cent bigger in radius. Orbiting close to its sun, its year is less than two weeks long; but because that star is so small and dim compared to ours, temperatures on the planet should range between zero and 40 degrees Celsius (about 30 to 100 Fahrenheit). Room temperature. Water should be liquid there, perhaps covering its surface with oceans ripe for life. At least, I hope it’s covered in oceans. Swimming would be easier than walking on a planet where the gravity is three and a half times that of Earth. The star is only 20 light years away from us; robot spaceships in the next 100 years or so could reach such a … Continue reading