ASTRONOMERS DISCOVER SUN’S TWIN AT McDONALD OBSERVATORY

FOR IMMEDIATE RELEASE

November 9, 2007

FORT DAVIS, Texas - Peruvian astronomers Jorge Melendez of
The Australian National University and Ivan Ramirez of The
University of Texas at Austin have discovered the best
“solar twin” to date, using the 2.7-meter Harlan J. Smith
Telescope at McDonald Observatory. Their findings suggest
that the Sun¹s chemical composition is not unique, as some
previously thought.

The star, HIP 56948, is more like the Sun than any yet seen,
and is 200 light-years away in the constellation Draco, the
dragon. The star may be a billion years older than the Sun.

Only three solar twins were previously known: 18 Scorpii,
HD 98618, and HIP 100963. But while they were all like the
Sun in many ways, there was one major difference: the amount
of lithium they contained. They all had several times more
than the Sun. Astronomers wondered if the Sun was unique in
its low amount of lithium.

The discovery of this new solar twin puts that question to
rest: it has the same low lithium content as the Sun. The
study turned up another solar twin, HIP 73815, that contains
a similarly low amount of lithium.

The question of chemical peculiarities in the Sun is related
to the “anthropic principle” — is there something special
about the Sun that has allowed life to spring up in our
solar system? Their findings don¹t answer that completely,
but they do show that when it comes to the Sun¹s chemical
composition, the answer is an emphatic “no.”

Melendez’ and Ramirez’ findings suggest the opposite,
so-called “Copernican” view: It is possible that life is
common elsewhere in the universe. They suggest that stars
like HIP 56948 would be good targets for SETI (Search for
Extra-Terrestrial Intelligence) researchers.

The star already has been studied by the McDonald
Observatory Planet Search led by University of Texas at
Austin astronomer Bill Cochran. His team found that, like
our Sun, HIP 56948 does not host any “hot Jupiter” planets,
those massive, short-period planets orbiting close to their
parent stars, so common among the more than 200 stars found
to date that host one or more planets.

Searches for “solar twins” are important because astronomers
use the Sun as a baseline for many other types of studies.
But they cannot study the Sun the same way they do the
distant stars. It’s too close, and too bright.

The solar twins discovered at McDonald will be useful for
many areas of astrophysics. In particular, they will help
astronomers who study the chemical compositions of stars, as
well as validate theoretical models of stars’ interiors, and
theoretical models of stellar evolution.

END

NOTE TO EDITORS: High-resolution artwork to accompany this
release is available online:

http://mcdonaldobservatory.org/news/releases/2007/1109.html