BBC NEWS Americas Africa Europe Middle East South Asia Asia Pacific
BBCi NEWS   SPORT   WEATHER   WORLD SERVICE   A-Z INDEX     

BBC News World Edition
 You are in: In Depth: San Francisco  
News Front Page
Africa
Americas
Asia-Pacific
Europe
Middle East
South Asia
UK
Business
Entertainment
Science/Nature
Technology
Health
-------------
Talking Point
-------------
Country Profiles
In Depth
-------------
Programmes
-------------
BBC Sport
BBC Weather
SERVICES
-------------
EDITIONS
San Francisco Tuesday, 20 February, 2001, 11:28 GMT
'Hungry' stars reveal planet presence
Planet outside the Earth's Solar System
There may be Earth-like planets out there. (Image Lynette Cook)
By Jonathan Amos in San Francisco

We may not have the means to detect them yet but there must be billions of Earth-like planets out there in our galaxy.

This striking suggestion emerges from a new statistical analysis of the light coming from nearby stars.


It's likely these stars still have material in orbit around them in the form of terrestrial-type bodies. There are planets there

Dr Norman Murray, astrophysicist
Dr Norman Murray, from the Canadian Institute for Theoretical Astrophysics, told a major science conference in the US that more than half the stars in his study showed evidence of having gorged themselves on rocky, iron-rich material.

This being the case, he said, it must be reasonable to assume these stars still had material in orbit about them, possibly in the form of planets the size of Earth.

High iron content

Detecting planets pushes current technology to its limits. Only about 55 planets have so far been discovered circling stars other than our own, and most of these are weird, giant planets that sit in unusual orbits.

Most astronomers concede that the direct detection of Earth-sized planets will require new techniques and next-generation telescopes. But Dr Murray told the annual meeting of the American Association for the Advancement of Science that an indirect, statistical method indicated that our galaxy was actually teeming with smaller planets.

"There is evidence that there is terrestrial-type material orbiting most of the stars in the solar neighbourhood," Dr Murray told the meeting. "So, the implication, if this result holds up, is that there are Earth-like bodies in orbit around most of the stars in our galaxy."

Dr Murray's study looked at more than 450 middle-aged stars like our Sun and about 20 that were entering old age. All were within about 325 light-years of Earth. The analysis indicated most had high iron content in their photospheres, or on their "surfaces".

System models

Based on what we knew about the way our Solar System behaved, Dr Murray said most of this iron would have come from lumps of rock like asteroids being hurled into the stars by the gravitational disturbance of orbiting planets.

"Something like 50% or higher of these stars have accreted more than an Earth-mass of terrestrial material [the Earth is about 30% iron]. In our Solar System, we believe the Sun has accreted about two-and-a-half Earth-masses of rocky material.

"Now, the implication here is that there must be something going on around those stars in order to accrete that amount of material, and we know from our own Solar System that this accretion process is not 100% efficient. Therefore, it's likely these stars still have material in orbit around them in the form of terrestrial-type bodies. There are planets there."

Dr Murray stressed there was no direct evidence these stars did have Earth-sized planets in orbit about them, but modelling had shown that if sufficient terrestrial material existed in a system it would eventually clump together into bodies as big as the Earth.

"I looked at just a tiny fraction of stars in the galaxy but there is no reason to believe that the particular stars I looked at are unusual in any way."

 WATCH/LISTEN
 ON THIS STORY
BBC science correspondent Pallab Ghosh
"There may be billions of Earth-like planets in the Milky Way"
See also:

22 Feb 00 | Washington 2000
26 Jan 99 | Anaheim 99
Internet links:


The BBC is not responsible for the content of external internet sites

Links to more San Francisco stories are at the foot of the page.


E-mail this story to a friend

Links to more San Francisco stories

© BBC ^^ Back to top

News Front Page | Africa | Americas | Asia-Pacific | Europe | Middle East |
South Asia | UK | Business | Entertainment | Science/Nature |
Technology | Health | Talking Point | Country Profiles | In Depth |
Programmes