Astronomers are excited about the discovery of the first multiple-planet solar system outside our own, writes Aaron Nicodemus
Announcement of a discovery of a multiple-planet system reminiscent of our own solar system has created excitement throughout the world, offering the first suggestion that planetary systems like our own are abundant.
The three planets, which rotate around the Upsilon Andromedae star, were discovered by a team of astronomers at San Francisco State University and independently confirmed by another team at Harvard University in Massachusetts.
The planets discovered most resemble Jupiter – large, gas- filled masses incapable of supporting life as we know it.
The planet closest to Upsilon Andromedae is about three- quarters the size of Jupiter and orbits the star once every 4,6 days. The middle planet, approximately twice the mass of Jupiter, takes 242 days to revolve around the star. And the outermost planet, a huge sphere approximately four times the size of Jupiter, completes one orbit every 3,5 to four years.
Approximately 20 planets have been discovered revolving around a star, but this is the first confirmed multiple- planet system outside our own. The discovery has astronomers scratching their collective heads, as it was previously deemed impossible for so many giant planets to form in one solar system.
Upsilon Andromedae is a bright star that will be visible to the naked eye from June. Its planets, however, are approximately 60 000 times too faint to be seen with the naked eye. In fact, astronomers with their high-powered telescopes cannot see them either; they merely observe how a star’s path is being affected by the bodies around it, and use that data to determine the presence of planets.
Dr David Laney, an astronomer at the South African Astronomical Observatory (SAAO)in Cape Town, says the method being used by the United States astronomers will only pick up large planets.
The US team used the Doppler method, which measures the speed at which a star is moving over a period of years. If a planet is moving around the star, “the tug of the planet’s gravity as it revolves around the star will make the star move slightly as well,” Laney explains. “If the planet is massive enough and close enough to the star, this Doppler method will allow us to tell that it’s there even though we can’t see it.”
Since this is currently the preferred method of finding planets, all of the planets discovered outside our solar system have been large planets that resemble Jupiter.
Laney and the team of astronomers at SAAO are using a different method to discover planets more like Earth. They are using a method called “gravitational lensing”, which operates under the theory that gravity bends light.
A small planet’s gravity can make a nearby star look brighter, as the planet’s gravity will magnify the light being given off by that star, Laney says. This week, the astronomers are looking at stars in the galactic bulge, searching for short spikes in the stars’ light curve that might indicate the presence of a small planet like Earth.
The SAAO is part of the Planet Collaboration, a group of observatories around the world tracking the same set of stars in the search for new planets. The observatories linked with the SAAO are in New Zealand, the US,Tasmania, Australia and the Netherlands.
Astronomer John Menzies says the collaboration is able to observe the stars 24 hours a day. “We hope one day we’ll witness a planetary event,” he said. “We’ll probably only have a few hours to see it, so we have to be at the ready.”
There is a drawback to the gravitational lensing method, Laney admits: “We can only see the planets once, and then we have to wait until the next time it passes in front of that particular star.” And how long might that be? “In some cases, more than a million years, and most astronomers aren’t that patient,” he says.
Picking out interesting stars in a field that is “carpeted in stars” is a tricky business, Laney says. “We have to carefully separate out the one star that is doing something. There are an incredible number of stars out there, and there’s a good chance that on any given night, one of them will be doing something interesting.”