Planet-like bodies with liquid water formed very early in the history of the
Solar System, or so scientists used to think. That scenario may now be due
for revision after a finding with ESA’s Infrared Space Observatory, ISO. The
theory was based on the presence of certain minerals called carbonates in
primitive Solar System objects. Carbonates are thought to form in liquid
water, which can only exist in large, planet-like bodies. Using ISO, an
international team has discovered large amounts of carbonates around two
dying stars, where large bodies do not exist. This suggests that carbonates
are not necessarily linked to liquid water. This is the first detection of
carbonates outside the Solar System.

“Our finding suggests that not all carbonates found in the Solar System were
formed in association with liquid water, and this of course sheds new light
on the formation history of the Solar System,” says Ciska Kemper, of the
University of Amsterdam.

The Solar System formed out of residual material left-over from the formation
of the Sun itself. About
5 000 million years ago ‘clumps’ in this material -which was swirling around
the newborn Sun – began to grow, and some ended up forming the planets.
Nowadays astronomers can study the earliest stages of the process by
analysing Solar System objects that are known to be very primitive, such as
certain meteorites. For instance, in several of these objects they have found
very old carbonates. This is considered to be evidence that large,
planet-like bodies with liquid water had ‘formed’ already 20 million years
after the
formation of the first clumps of material around the Sun.

Liquid water is thought to be a key ingredient for the formation of
carbonates. On Earth, a large fraction of sedimentary rocks are carbonates –
for instance, limestone and marble. They are the sediments that precipitate
when a watery solution of carbon dioxide and another mineral, such as
calcium, becomes saturated – the ‘scale’ in the tea kettle forms in the same
way. Carbonates exist also in grains of dust between the planets, in
asteroids and in meteorites coming from Mars, for example, in the famous
meteorite ALH 84001, which some say contains fossilised bacteria.

However, ISO’s discovery, for the first time, of carbonates in dying stars
breaks the automatic association between these minerals and liquid water.
Kemper and her colleagues have found large amounts of the carbonates calcite
and dolomite in the nebulae NGC 6302 and NGC 6537, dubbed respectively the
‘Bug Nebula’ and the ‘Red Spider Nebula’. These are old stars that have spent
the last ten thousand years expelling material through dense stellar winds
and are about to ‘die’ as white dwarfs – small, very dense and opaque
‘corpses’ of stars. It is in the expelled material, which now forms a shell
around the central star, where ISO has identified the unmistakable chemical
signature of the carbonates, their spectra. And these carbonates cannot have
been formed through the interaction with liquid water: neither has the
material from the stars condensed to form new planets, nor are the
carbonates residual from a pre-existing planetary system destroyed by the
dying star.

“The amount of carbonates we find is equivalent to at least 30 Earth masses,
far too large to be the relic of a hypothetical planetary system present
before the star became a planetary nebula. On the other hand, the age of the
dust-shell in the nebula is about ten thousand years, which is too short for
a new planetary system to form,” explains Kemper.

Therefore, the carbonates around the Bug Nebula and the Red Spider Nebula
must have formed through an alternative mechanism that does not involve
liquid water. Kemper and colleagues suggest several possibilities but say
none of them has been tested in the laboratory yet.

Was this alternative mechanism also at work in the early Solar System? The
authors cannot say. But the mere possibility implies that the assumption that
carbonates in primitive Solar System objects indicates the quick formation of
planets with liquid water in the Solar System needs to be reviewed.

For more information please contact:

Science Programme Communication Service, ESA

ESTEC- Noordwijk, The Netherlands

phone: + 31(0)71.565.32.73

fax: + 31(0)71.565.41.01

Scientific contact

Dr. Leo Metcalfe – ISO Project Scientist

ISO Data Centre – Madrid, Spain

phone: +34(0)

fax: +34(0)

About ISO

The European Space Agency’s infrared space telescope, ISO, operated from
November 1995 until May 1998, almost a year longer than expected. As an
unprecented observatory for infrared astronomy, able to examine cool and
hidden places in the Universe, ISO successfully made nearly 30 000
scientific observations.
More information about ISO can be found at .

Images for this News Release are available at

These ISO results will be published in the 17 January 2002 issue of the
scientific journal Nature.