An artist's impression of the three planets in orbit around Upsilon Andromedae. The first is a large gas giant with rings at right, the second appears as a small dark circlein the centre, and the third is a spot seen on top of the yellow glowing star. Image: Lynette R. Cook, San Francisco State University.
A schematic diagram of the orbits for the 3 planets detected around
Upsilon Andromedae. The red dots mark the orbits of components b,c and
d. The dashed circles show the orbits of Mercury, Venus, Earth
and Mars (inside to outside, respectively) overplotted to give a
sense of the scale of the extrasolar planetary orbits. Jupiter, at
5 AU would be outside the boundaries of this
|From: Stig Agermose <email@example.com>
Source: Astronomy Now's webpage on breaking news:
First system of multiple planets found around a sun-like starSAN FRANCISCO STATE UNIVERSITY NEWS RELEASE
April 15, 1999
SAN FRANCISCO, April 15, 1999 Astronomers from four research institutions
have discovered strong evidence for a trio of extrasolar planets that orbit
the star Upsilon Andromedae. This is the first multiple planet system ever
found around a normal star, other than the nine planets in our Solar System.
The closest planet in the Upsilon Andromedae system was detected in 1996
by San Francisco State University (SFSU) astronomers Geoffrey Marcy
In parallel, astronomers from the Harvard-Smithsonian Center for
This first planetary system, found from a survey of 107 stars, offers the first suggestion that planetary systems like our own are abundant in our Milky Way Galaxy, which contains 200 billion stars. SFSU researcher Debra Fischer said, "It implies that planets can form more easily than we ever imagined, and that our Milky Way is teeming with planetary systems."
The innermost (and previously known) of the three planets contains at least three-quarters of the mass of Jupiter and orbits only 0.06 AU from the star. (One "AU" equals the distance from the Earth to the Sun). It traverses a circular orbit every 4.6 days. The middle planet contains at least twice the mass of Jupiter and takes 242 days to orbit the star once. It resides approximately 0.83 AU from the star, similar to the orbital distance of Venus. The outermost planet has a mass of at least four Jupiters and completes one orbit every 3.5 to 4 years, placing it 2.5 AU from the star. The two outer planets are both new discoveries and have elliptical (oval) orbits, a characteristic of the nine other extrasolar planets in distant orbits around their stars.
No current theory predicted that so many giant worlds would form around
a star. "I am mystified at how such a system of Jupiter-like planets might
have been created," said Marcy, SFSU's Distinguished Professor of Science.
This will shake up the theory of planet formation." Robert Noyes, a professor
of astronomy at Harvard-Smithsonian CfA and a member of the
Currently a staff astronomer at the Anglo-Australian Observatory, Butler,
an American, is the lead author of the paper, submitted to the
Marcy and Butler had suspected that there was something strange about
Upsilon Andromedae. The velocity variations that revealed the closest planet
to the star in 1996 had an unusual amount of scatter. Not until early this
year had enough observations been made of the star to confirm the presence
of an additional planet, which explained some of the confusing pattern
in the data. But another object still seemed to be tugging on the star.
"We looked at the two planet solution that we had been expecting and there
was still too much extra noise," said Fischer. "We arrived at the conclusion
that the extra observed wobble could only be explained by the presence
of a third planet." Both teams of astronomers considered
One big question left to answer is how such a solar system arose. "The
usual picture is that gas giant planets can only form at least four AU
away from a star, where temperatures are low enough for ice to condense
and begin the process of planet formation," said Brown. "But all three
giant planets around Upsilon Andromedae now reside inside this theoretical
ice boundary." The planets may have formed close to the host star, or,
like balls on a billiard table, the planets may have scattered off of each
other, migrating into their current orbits from a more distant place of
The discovery of this multiple planet system suggests a new paradigm for planet formation where many small seed planets known as planetesimals might develop in the disk of matter surrounding a star. Those planets that grow fastest would engage in a gravitational tug of war that weeds out some of the smaller worlds and determines which planets ultimately remain in orbit.
"The Upsilon Andromedae system suggests that gravitational interactions between Jupiter-mass planets can play a powerful role in sculpting solar systems," said Butler.
If these Jupiter-mass planets are like our own Jupiter, they would not be expected to have solid Earth-like surfaces. But, Nisenson noted, "Our observations can't rule out Earth-sized planets as well in this planetary system, because their gravity would be too weak for them to be detectable with present instruments."
A bright star visible to the naked eye starting this June, Upsilon
San Francisco State University is a highly diverse community of 27,000
students and 3,500 faculty and staff. It is one of the largest campuses
in the nationally recognized 23-campus California State University system.
Founded in 1899, the University is celebrating its 100th year of service
to San Francisco, the Bay Area and beyond. The Harvard-Smithsonian Center
for Astrophysics, located in Cambridge, MA, is a joint collaboration between
the Smithsonian Astrophysical Observatory and the Harvard College Observatory.
Return to UFO Folklore !