Date: Fri, 28 Apr 2000 15:26:34 GMT
From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
Subject: ISO Measures Possible Planetary System In Formation
ESA Science News
27 Apr 2000
ISO measures possible planetary system in formation
The earliest stages of formation of planetary systems remain very poorly
known because of the thick layers of opaque dust that hid them. The
European Space Agency's infrared space telescope, ISO, has measured the
size of a proto-planetary system, surrounding a newly-born star, a Spanish
team of astronomers report in tomorrow's issue of the journal Science. ISO
sees a very young 'baby-star' surrounded by a disk of the same diameter as
Jupiter's orbit, in which planets are likely to form in the future.
Stars are born within thick 'cocoons' of dust very difficult to penetrate, and
for this reason current models describing the process are very incomplete.
Astronomers know, in broad terms, that the future star begins to form within
the dust cloud by accreting material which forms a disk, the same disk out of
which planets, comets and all the components of a planetary system will
probably form in the future -- the disk is actually called a 'protoplanetary
disk'. Once the star-to-be has gathered enough material, the high pressures
and temperatures in its centre trigger the first nuclear reactions and the
star 'lights up' -- it starts the 'ignition'. During this process the very
star or 'protostar' emits jets of material that can be detected with different
techniques. Astronomers use these detectable signs to classify the
evolutionary stages of the new-born stars.
The system observed by ISO was previously thought to be at the earliest
evolutionary stage, in fact, so young that the protostar had not yet had time
to ignite. However, ISO results contradict this belief.
"We are seeing the earliest stages of formation of a planetary system. There
is already a central object hot enough to work as a star and to heat up its
surrounding protoplanetary disk. The star is already 'lit up'", says Spanish
astronomer Jos=E9 Cernicharo, from the Instituto de Estructura de la Materia
(CSIC), in Madrid, main author of the article being published in Science.
The system observed by ISO's infrared camera, ISOCAM, is 1200 light years
away in a star-forming region in the Orion nebula. It's called VLA1/2.
Cernicharo and his group estimate that the central star and its surrounding
matter might be at an average temperature of at least 500 degrees Kelvin.
It is surrounded by a protoplanetary disk whose diameter is four times the
distance from the Earth to the Sun, the same as Jupiter's orbit.
"This is the first time we can determine the size of the regions where
where a low mass star and its planets are being formed", Cernicharo says.
ISO was also able to analyse the chemical composition of the large cocoon
of material enshrouding both the star and its protoplanetary disk, a
structure called by the researchers the 'placental' envelope. It is much
colder, and made up of grains of dust covered by ices of water, carbon
dioxide, methane and probably methanol. This chemical information, another
'first' of the work, will contribute substantially to understanding the
star-birth processes, say the researchers.
ISO results also indicate -- as highlighted by the team in Science -- that
these systems will be observable with the new generation of large (8 metre
class) ground-based infrared telescopes. Current knowledge so far suggested
that these very dusty objects could only be detected at far-infrared
wavelengths not accessible from the ground, but ISO has shown that they
can also be seen at certain very precise infrared wavelengths which do
indeed cross the Earth's atmosphere -- the so-called 'infrared windows' at
which ground-based infrared telescope work.
For this work, ISO observations were complemented with the 30 metres
radio telescope of the Institute de Radioastronomie Millim=E9trique (IRAM),
in Granada (Spain).
Footnote about ISO
The European Space Agency's infrared space observatory, ISO, operated from
November 1995 to May 1998, almost a year longer than expected. An
unprecedented observatory for infrared astronomy, able to examine cool and
hidden places in the Universe, ISO made nearly 30,000 scientific observations.
Jos=E9 Cernicharo, Instituto de Estructura de la Materia (CSIC)
Tel: +34 91 5901611
Martin F. Kessler, ISO Project Scientist
Tel.: + 34 91 813 1253
USEFUL LINKS FOR THIS STORY
* ISOCAM homepage
* ISO Science homepage
* SCIENCE journal
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