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star watch

As 715 new planets announced, Jupiter shines high in the sky

The stars don’t change from year to year, at least for naked-eye skywatchers, but the planets are always moving around. They combine with the constellation patterns they pass through to form new patterns that morph and disappear.

This winter, for instance, big Jupiter shines high and bright in the clear evening sky, truly the king of planets. You can’t miss it if you take a moment to face south and look high.

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The second-brightest point these evenings is Sirius, the Dog Star, in the south far below Jupiter. These form the top and bottom of a temporary constellation that we can call the Winter Diamond. Its two side corners are Procyon, the Little Dog Star, and Betelgeuse in one shoulder of Orion.

The Winter Diamond is huge. It looks much bigger in the sky than here in the drawing. Face south on a clear evening and it will practically jump out at you.

Most winters it’s not there. Last year Jupiter shone outside the right of the frame here, and next year it will be outside the left edge. And then for the next 10 years it will be gone from the area completely, leaving Sirius, Procyon, and Betelgeuse to form the better known Winter Triangle by themselves.

A Kepler planet bonanza

We’re lucky to live in a solar system with several bright planets that lend variety to our night sky. But we’re learning now that some solar systems probably have a lot more planets than we do.

Astronomers in the last two decades have turned a big corner. They’ve settled a question that people wondered and speculated about since at least the ancient Greeks: Does the universe hold many other worlds? The answer turns out to be a resounding yes. Most of the stars you see on a dark night, and most of the quadrillions beyond, harbor worlds of their own.

Much of this knowledge has come from one instrument: NASA’s Kepler planet-hunting telescope, far above Earth’s atmosphere. It performed with spectacular success for nearly four years until a mechanical failure last May stopped it from functioning.

Still in progress is the task of analyzing the data Kepler collected. Last Wednesday, Kepler’s science team held a press conference to announce what NASA called “a planet bonanza.” The Kepler analysts used an indirect method to confirm the existence of 715 more planets orbiting 305 stars in the constellations Cygnus and Lyra. This single announcement hiked the tally of exoplanets confirmed since 1992 from about 1,000 to 1,700.

Kepler worked by watching stars for tiny dips in brightness caused by planets passing across the face of stars. The latest new worlds come from an indirect analysis that the astronomers decided was good enough for ruling out false alarms where two or more planets are seen crossing the same star.

Most of the newly confirmed finds are moderately smallish worlds, in the interesting size range from Neptunes down through super-Earths to near-Earths. Most are unpleasant places: They’re broiling-hot roasters close to their suns. This is not because most planets are hot, but simply because planets very close to their suns are the easiest ones to find. Similar numbers probably orbit a little farther out, where temperatures are more friendly.

The abundance of smallish worlds firms up a conclusion that astronomers had already reached: The smaller the planets, the more of them there are. If you made classroom models of all 1,700 on the confirmed list and spilled them across the floor, the Earth-size marbles would outnumber the golf-ball Neptunes, and the golf balls would outnumber the Jupiter baseballs and the super-Jupiter softballs. This size trend — the smaller the commoner — is so clear that it probably applies throughout the universe. Commented MIT exoplanet researcher Sara Seager at the Wednesday press briefing: “Nature wants to make small planets.”

We don’t know yet whether this trend continues down to pea-size Marses and BB-size bodies like our moon. Even Kepler was not sensitive enough to get reliable statistics on globes so small.

It’s not over. Wednesday’s planet haul came from Kepler’s first two years of data. The analysis requires massive computing power, and the science team estimates that hundreds more worlds remain to be extracted and confirmed from Kepler’s later brightness measurements.

And it’s sobering to think that for all this time, Kepler was watching only one four-hundredth of the sky. Even there, it saw only a few thousand light-years into space, at most. A whole lot of worlds are out there.

Whole-sky maps

Easy-to-use maps of stars in the evening sky are available
at SkyandTelescope.com/
gettingstarted.

Alan M. MacRobert is a senior editor of Sky & Telescope magazine in Cambridge (SkyandTelescope.com). His Star Watch column appears the first Saturday of every month.
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