SETI [ASTRO] Big Star Ate My Planet

Larry Klaes (
Thu, 03 Jun 1999 11:16:45 -0400

>X-Authentication-Warning: majordom set sender to owner-astro using -f >Date: Thu, 3 Jun 1999 0:20:48 GMT >From: Ron Baalke <> >To: >Subject: [ASTRO] Big Star Ate My Planet >Sender: >Reply-To: Ron Baalke <> > >New Scientist > >UK Contact: >Claire Bowles,, 44-171-33-2751 > >US Contact: >New Scientist Washington office,, 202-452-1178 > >EMBARGOED FOR RELEASE: June 2, 1999, 2 p.m. EDT > >Big star ate my planet > >GIANT planets orbit up to 8 per cent of all Sun-like stars, say astronomers >in the US. The estimate comes not from counting planets directly, but from >counting stars that appear to be swallowing planets. > >When stars such as the Sun exhaust the hydrogen fuel in their centres and >become bloated "red giants", they grow big enough to swallow any closely >orbiting planets. This won't happen to the Sun for another 5 billion years or >so. But Mario Livio and Lionel Siess of the Space Telescope Science Institute >in Baltimore, Maryland, reason that since the red giant phase lasts a few >hundred million years, other Sun-like stars should be gobbling up their >planets at this very moment -- yielding clues about how many planets are >out there. > >They simulated what would happen if giant planets with masses comparable >to that of Jupiter were gobbled by their stars, and found three strong markers. >First, planet eaters glow with an excess of infrared light, as gravitational >energy dumped into the star by the planet heats up the star, causing it to >expand and puff off its cool outer layers as expanding shells of dust. Second, >angular momentum transferred from the planet speeds up the spin of normally >sluggish red giants to about 10 per cent of the speed at which they will >eventually fly apart. Finally, the planet contaminates the star with lithium, >an element that does not normally survive for long in the heat of a star. > >Remarkably, Livio and Siess say that many red giants show all of these >telltale signs: they are spinning very rapidly, emitting anomalous amounts >of infrared and their light shows the spectral "fingerprint" of lithium. "We've >found that about 4 to 8 per cent are showing the signs of swallowing planets," >says Livio. "This percentage agrees very well with more direct estimates >of the prevalence of planets." Livio and Siess's work will be published in >Monthly Notices of the Royal Astronomical Society. > >Other astronomers are impressed. "The planet-swallowing hypothesis is the >best explanation I've seen for the origin of these lithium-rich giants," says >Caty Pilachowski of the National Optical Astronomy Observatories at Kitt >Peak in Arizona. The work also highlights the fact that planets can have a >profound effect on the evolution of stars, she says. > > ### > >Author: Marcus Chown >New Scientist issue 5 June 1999 > >PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS ARTICLE - THANK YOU > >

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