Solar systems like ours - NRC Publications Archive

NRC Publications Archive
Archives des publications du CNRC
Solar systems like ours
Tapping, Ken
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. /
La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version
acceptée du manuscrit ou la version de l’éditeur.
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien
DOI ci-dessous.
Publisher’s version / Version de l'éditeur:
http://doi.org/10.4224/23000187
Skygazing: Astronomy through the seasons, 2014-09-23
NRC Publications Record / Notice d'Archives des publications de CNRC:
http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=8802e11e-519d-4fc1-aed9-64b3696813e3
http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=8802e11e-519d-4fc1-aed9-64b3696813e3
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/copyright
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site
http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/droits
LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
Questions? Contact the NRC Publications Archive team at
[email protected]. If you wish to email the authors directly, please see the
first page of the publication for their contact information.
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la
première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez
pas à les repérer, communiquez avec nous à [email protected].
SOLAR SYSTEMS LIKE OURS
Ken Tapping, 23rd September, 2014
Thanks to improved telescopes and other
astronomical instruments, we now know that most
stars have planets. At first we could only detect
really large planets, like Jupiter, but now we are
finding planets the size of the Earth. Our ideas
about the formation of stars suggest that whenever
a star forms, a retinue of planets is formed too.
However, most of the planetary systems we find
orbiting other stars are bizarrely different from
ours, which we refer to as the Solar System.
We expected that those other planetary systems
would be more or less like ours: small, rocky
planets close in, and large, gas giant planets
further out. This logical concept is centuries old.
Pierre-Simon Laplace, the French astronomer and
mathematician formulated it in the late 18th
Century. The idea is that stars and planetary
systems form from the collapse of a cloud of
cosmic gas and dust. The cloud forms a disc,
which then forms a star at the centre and planets
orbiting it. The radiation from the newborn star
evaporates volatile materials from the nearer
planets, leaving them as small rock balls. Further
out, those materials are not evaporated, so the
planets are larger, and mostly consisting of gas. In
the Solar System, the rock balls are Mercury,
Venus, Earth and Mars, and the gas giants are
Jupiter, Saturn, Uranus and Neptune. The picture
is logical and we expected it everywhere else.
That’s not what we found. In many cases we have
found gas giant planets orbiting extremely close to
stars; in some cases so close they take days to
complete one orbit. Mercury, the closest known
planet to the Sun takes 88 days, and Jupiter, the
gas giant planet closest to the Sun takes 12 years.
It’s likely that a gas giant planet close to a star will
have its gases and other volatile material cooked
off in a short time – in astronomical terms. So
there are two rather disquieting issues here: firstly
how can the orbits of planets be so drastically
changed, and secondly, it cannot have been that
long ago, because by now the planet would have
become a rock ball.
Our Solar System formed about 4.5 billion years
ago. The oldest rocks on Earth that bear evidence
of living things were laid down about 3.5 billion
years ago. We believe that life as we know it
began in the sea and required permanent oceans
to survive and evolve. It appears that life appeared
on Earth as soon as the planet had cooled enough
for water to accumulate on its surface. Since even
a tiny change in the Earth’s distance from the Sun
could freeze or fry us, we can assume that nothing
drastic has happened to the Earth’s orbit for at
least the last 3.5 billion years – most of the life of
the Solar System. It has been suggested that ice
ages are caused by really microscopic changes in
the Earth’s orbit. This stability does not fit well with
what we are seeing with other planetary systems.
This has led to an increasing effort to research the
behaviour of multiple planets orbiting a star.
The physics is relatively simple; we have several
bodies tugging at each other with their gravity.
The problem is that the simple calculations have to
be done millions or billions of times. However,
computers are really good for this sort of work. The
results are somewhat disquieting, in that they
show planets perturbing each other into dramatic
changes in their orbits. The calculations bear out
what we are seeing with other planetary systems.
This is leading to extensive work into modelling the
history of the Solar System, to see what sort of
juggling act might have gone on, which still left our
planet alone for at least 3.5 billion years.
The Sun crosses the celestial equator on the 22nd,
marking the Autumn Equinox. Venus is getting lost
in the sunrise glare. Jupiter rises in the early
hours. Saturn and Mars lie close together, very low
in the sunset twilight. The Moon will be New on the
23rd and will reach First Quarter on 1st October.
Ken Tapping is an astronomer with the National
Research Council's Dominion Radio Astrophysical
Observatory, Penticton, BC, V2A 6J9.
Tel (250) 497-2300, Fax (250) 497-2355
E-mail: [email protected]