Multiple planets circle many other stars
Multiple planets circle many other stars
August 7, 2000 - BBC
Astronomers have found nine new planets circling nearby stars, an astronomical conference was informed on Monday.
It brings the total number of planets discovered circling other stars, so-called exoplanets, to 50.
The second known example of a star orbited by more than one planet was also announced.
It could be the first of many as scientists say they are now seeing the first tantalising hints that multiple planets may circle many other stars.
The rush of new planetary announcements comes on top of Friday's news of an exoplanet around Epsilon Eridani. At a mere 10.5 light years from Earth, this world could be visible to the Hubble Space Telescope.
Saturn-sized planets
During the last five years, 41 exoplanets had been detected orbiting nearby stars, but until now only one system, Upsilon Andromidae, had been shown to have more than one planet going round a sun.
Prof Geoff Marcy of San Francisco State University said, "We are finding planets faster than we can investigate them".
It brings the total number of planets discovered circling other stars, so-called exoplanets, to 50.
The second known example of a star orbited by more than one planet was also announced.
It could be the first of many as scientists say they are now seeing the first tantalising hints that multiple planets may circle many other stars.
The rush of new planetary announcements comes on top of Friday's news of an exoplanet around Epsilon Eridani. At a mere 10.5 light years from Earth, this world could be visible to the Hubble Space Telescope.
Saturn-sized planets
During the last five years, 41 exoplanets had been detected orbiting nearby stars, but until now only one system, Upsilon Andromidae, had been shown to have more than one planet going round a sun.
At the International Astronomical Union (IAU) General Assembly being held in Manchester, UK, scientists reported the discovery of a second extra-solar planetary system.
It contains two Saturn-sized planets orbiting a star called HD 83443. This star is slightly less massive than our Sun (0.8 solar masses).
It lies in the constellation Vela and is 141 light years away from our Solar System. The two gas giant planets both orbit very close to the star. One of them orbits the star in 2.98 days, the other in 29.8 days.
Astronomers are at a loss to explain why one circles the star almost exactly 10 times faster than the other. The inner planet has the shortest orbital period and has the smallest distance from its parent star than any other exoplanet yet discovered.
Unexplained wobbles
The number of stars found to have more than one planet in orbit about them is set to grow rapidly.
A team of astronomers based at the University of California, Berkeley, is beginning to detect hints that many extrasolar planets may have smaller companions.
Dr Debra Fischer, of the University of California at Berkeley, has looked at data for 12 stars around which single planets are known to circle.
She says she is beginning to see patterns that these planets may have siblings. Of the 12 stars she has looked at, she has found that five exhibit unexplained wobbles that could result from the tug of a companion - whether another planet, an unseen star or something in-between.
"This is the first time anyone has noticed that such a high percentage of stars with one known planet show evidence of a second companion," Fischer said.
Signature in the dust
"We're now at a stage where we are finding planets faster than we can investigate them and write up the results," said Professor Geoff Marcy of San Francisco State University. "It's wonderful. Planet hunting has morphed from the marvellous to the mundane."
Nasa astronomers also reported to the IAU conference that they have studied the patterns imprinted on the dust disks around well known, nearby stars to determine whether they have orbiting planets.
The planets are still hidden but they write their signature in the dust, say the researchers. The astronomers estimate that the Beta Pictoris star has a planet 10 times the mass of Earth orbiting at a distance of about 10.4 billion km (6.5 billion miles). And Vega, one of the brightest objects in the sky, appears to have a planet twice the mass of Jupiter in an orbit about 8 billion km (5 billion miles) from the star.
These distances from the parent star are larger than for any of the planets in our Solar System.
Earth-like clones
The exoplanets so far discovered have forced astronomers to think long and hard about their theories of how planets form around a central star.
Professor Marcy told the BBC: "The planets we are finding about other stars all orbit in elongated, elliptical orbits. It's quite frightening that virtually all the planets we've found orbit close to their stars where they heat up and then move out to where they cool down.
"Water would boil and then freeze - and of course, such characteristics are not conducive to life."
But Professor Marcy remains confident that Earth-like planets will be found. "There must be rocky planets out there that have just the right temperature so that the water is not frozen into ice nor vaporised into steam but is in liquid form," he said.
"It may be that our Solar System is one in a hundred or one in a thousand, but let's not forget that our Milky Way galaxy contains one hundred billion stars so there are certainly Earth-like clones out there."
August 4, 2000 - BBC
Astronomers have discovered a planet orbiting the star Epsilon Eridani.
The relative proximity to Earth - a mere 10.5 light years - means this is the closest star yet to have a planet found circling about it.
This raises the exciting possibility that the Hubble Space Telescope may be able to obtain an image of the planet.
If that is possible, it would be an astronomical landmark as it would be the first planet actually seen circling another star.
The discovery will be announced at an astronomical conference in Manchester on Monday.
Larger than Jupiter
The planet orbiting Epsilon Eridani, a star very similar to our own Sun, was found by a team led by Dr William Cochran, of the University of Texas McDonald Observatory.
The planet orbits Epsilon Eridani from a distance of about 500m km (300m miles) - roughly the distance from the Sun to the asteroid belt in our own Solar System.
Researchers estimate that the planet of Epsilon Eridani is probably just larger than Jupiter, the largest planet in our Solar System.
Epsilon Eridani is a star slightly less massive than our Sun and slightly cooler.
It is most probably younger as well, being only about one billion years old compared with our Sun's age of 4.5bn years.
Viewed from Earth
It may be possible to view the planet with the Hubble Space Telescope or with the new generation of advanced imaging systems connected to ground-based telescopes.
If the planet could be seen as a tiny speck of light next to the artificially suppressed image of its parent star, it would be a major scientific achievement - the first time an image of a planet circling another star would have been obtained.
With such an image, astronomers could analyse the light from the planet and determine its physical characteristics and composition.
To date, current imaging technology has forced astronomers to use indirect methods to detect the presence of planets around stars. This can involve looking for a tell-tale "wobble" in the parent star - behaviour that can be explained only by the gravitational effects associated with a planet-sized body circling nearby.
May 9, 2000 - BBC
Eight new "planets" have been discovered by Swiss astronomers.
Their detection brings to about 40 the number of known planets outside our Solar System.
The present discoveries complete and enlarge our still preliminary knowledge of extra-solar planetary systems, as well as the transition between planets and brown dwarfs.
The objects, which are circling stars similar to our own Sun, have masses that range from less than that of Saturn to about 15 times that of Jupiter.
The discoveries were made using a 1.2-metre telescope at the European Southern Observatory's La Silla complex in South America.
The planets were picked up by the now standard radial velocity technique that has discovered most of the known so-called exoplanets.
Brown dwarfs
This hinges on detecting changes in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. In other words, the star appears to wobble under the influence of its smaller companion.
La Silla is on the southern extremity of the Atacama desert in Chile
The new objects are quite diverse. Six of them are most likely bona fide exoplanets. The other two are apparently very low-mass brown dwarf stars. These are objects that do not have sufficient mass to trigger the type of nuclear reactions that make other stars shine.
"The present discoveries complete and enlarge our still preliminary knowledge of extra-solar planetary systems, as well as the transition between planets and brown dwarfs", said planet hunters Michael Mayor and Didier Queloz from the Geneva Observatory.
One of the new planets has just 80% of the mass of Saturn. This is only the third exoplanet detected so far with a possible sub-saturnian mass. It was picked up orbiting a Sun-like star called HD 168746.
Positioned in the constellation of Scutum (the Shield), HD 168746 is located at a distance of about 140 light-years (1,300 million, million kilometres). The planet goes around the star every 6.4 days, a fairly short period.
Hot planet
Another very interesting world was detected around a star called HD 83443 in the constellation Vela - the Sail. It is 141 light years away.
It has a mass just greater than that of Saturn and the shortest orbital period (2.986 days) and the smallest distance to the central star (5.7 million km) so far discovered.
Being so close to its star, the exoplanet must be heated to a temperature of many hundreds of degrees.
There are also indications that there could be an even smaller body in this system.
Jupiter is about 317 times more massive than the Earth and Saturn is about 95 times more massive.
The San Francisco State University Planet Search Team independently announced one of the new planets last week.
December 1, 1999 - Reuters - San Fran
Astronomers have found evidence of six new planets orbiting distant stars, bringing to 28 the planets known to exist outside of the solar system.
An international team of astronomers announced Monday that all the newly discovered planets are about the size of Jupiter or larger, and they all orbit stars 65 to 192 light years from Earth.
At least five of them, given their distance from their stars, could have liquid water, a fundamental requirement for life, the researchers said. The planets' presence was discovered by measuring a very slight motion distortion, or wobble, of the target star. The wobble is caused by the gravitational pull from a planet that orbits the star.
The astronomy team includes Steven Vogt of the University of California, Santa Cruz; Geoffrey Marcy of the University of California, Berkeley; Paul Butler of the Carnegie Institution of Washington, and Kevin Apps of the University of Sussex, England. The group discovered many of the other extrasolar system planets. A report on their findings will be published in the Astrophysical Journal.
All of the newfound planets are thought to be giant balls of hydrogen and helium gas, similar to Jupiter.
Most of the extrasolar planets circle their parent stars in eccentric, oval-shaped orbits. One of the newly discovered planets dips to within 36 million miles of its star and then swings out to more than 214 million miles.
"It is beginning to look like neatly stacked, circular orbits such as we seen in our own solar system are relatively rare," Vogt said in a statement.
The Earth orbits the sun in an almost circular orbit of about 93 million miles. The Earth-to-sun distant is called an astronomical unit, or AU, and is a value astronomers use to express planetary distances.
Five of the six new planets are within what is called the habitable zone. This is a region around a star where temperatures would allow liquid water to exist. Planets and moons inside the habitable zone are thought to be too hot for liquid water, and those outside the zone are thought to be too cold.
"These planets are at just the right distance, with temperatures in one case around 108 degrees F - like a hot day in Sacramento," said Vogt.
It is unlikely that an Earth-sized planet could coexist with the newly discovered planets, said Vogt. The presence of the Jupiter-sized planets at their orbital distance from the host stars would cause smaller planets to be ejected from around the star. This does not happen to the Earth because Jupiter orbits far outside the Earth's orbital path.
Any moons orbiting the planets within the habitable zone, said Vogt, "offer the possibility of liquid water and the eventual emergence of life."
Details on the newly found planets, with the name of the host star, its distance from Earth, the planet size and its estimated average temperature (a light year is 5.9 trillion miles; Jupiter's mass is about 318 times greater than that of Earth):
November 15, 1999 - AP
A startling image of a planet passing in front of a bright star has confirmed what scientists before only could deduce with math - there are planets beyond our solar system.
``This is the first independent confirmation of a planet,'' said Geoffrey Marcy, a professor of astronomy at the University of California at Berkeley. ``It also gives us the first-ever measure of the size of one of these planets.''
Marcy's planet-hunting team had gathered mathematical evidence of 19 planets but could only infer their existence by measuring the wobble of nearby stars caused by the planets' gravity as they orbit.
That changed last week.
Marcy and his colleagues first detected a wobble in the star HD 209458, in the constellation Pegasus, on Nov. 5 from the Keck Telescope atop Hawaii's Mauna Kea.
The team notified astronomer Greg Henry of Tennessee State University, who operates a cluster of remote-controlled telescopes in the Patagonia Mountains of Arizona.
Henry focused one automatic telescope on the star, and observed it dimming visibly as the planet crossed in front of it - just as Marcy's scientists had predicted.
The star's radiance dimmed 1.7 percent on Nov. 7. On Thursday, it happened again, seemingly verifying the scientists' calculations that the planet orbits its star every 3.523 days. Henry is predicting the same dimming next Thursday and again Nov. 22.
``We've essentially seen the shadow of the planet,'' Henry said.
Marcy's team determined the planet to be a ``gas giant,'' similar to Jupiter, but its mass is just 63 percent of Jupiter's while it is 60 percent wider.
A gas giant could not have formed so close to a star, Henry said, which supports the theory that ``extra-solar planets very near their star did not form where they are, but formed farther out and migrated inward.''
The star HD 209458 lies 153 light-years from Earth - almost a million billion miles. It is near the star 51 Pegasi, around which the first extra-solar planet was discovered in 1995.
``With this one, everything hangs together,'' Marcy said. ``This is what we've been waiting for.''
September 14, 1999 - BBC Online
A chance alignment between two stars may have allowed astronomers to detect the first Earth-sized planet found outside our solar system.
In June 1998 observations made at the Mount Stromlo Observatory in Australia and the Mount John Observatory in New Zealand detected a star near the centre of our galaxy becoming abnormally bright.
The brightening occurred because of the so-called gravitational lensing effect. This happens when another star passes directly between the distant star and ourselves.
Its gravity acts like a lens bending and amplifying the light from the distant object. The observatories were looking for just such an event.
By studying the way the distant object's light rises and falls, astronomers could determine the distant star appeared to be larger than our own Sun.
A detailed analysis of the data suggests the light-curve can only be explained if it has a planet orbiting it.
If so then it must be the smallest planet discovered orbiting another star - possibly as small as the Earth.
Different techniques
In the past few years astronomers have discovered about 20 planets orbiting some of the nearest stars to our Sun using different techniques.
All of them however have been massive and are probably more like the gas giant Jupiter than the small, rocky Earth.
This new planetary system would be unique in not having any gas giant planets. A detailed analysis has been submitted for publication in the Astrophysical Journal.
More recent observations of another star brightening suggest the same group of astronomers may have discovered a planet in a large orbit around two close stars.
June 3, 1999 - Albequerque Journal
Scientists using a New Mexico telescope have discovered two overgrown planets drifting alone in empty space -- the first such objects ever found.
More massive than Jupiter but too small to burn like our sun, the planetlike orbs represent a new type of extremely faint space object that scientists say may be as common as the stars in our galactic neighborhood.
Their discovery demonstrates the power of the New Mexico-based Sloan Digital Sky Survey, said Johns Hopkins University astronomer David Golimowski.
Golimowski and Princeton University astronomer Xiaohui Fan announced the discovery of the new objects, called "methane dwarfs," during this week's meeting of the American Astronomical Society.
Each is "too small to be a star but probably too large to be called a planet," Fan said. But while Jupiter and other similar objects have been found orbiting stars, Fan's methane dwarf was all by itself in empty space.
Soon after Fan's discovery in early spring, Golimowski found a second methane dwarf in data collected by the Sloan telescope.
Follow-up observations with telescopes in New Mexico and Hawaii showed methane in their atmospheres, as in the atmosphere of Jupiter. The scientists have only a rough idea of the objects' size but estimate they're 10 to 70 times the mass of Jupiter, the largest planet in our solar system. That's at most 7 percent the size of our sun.
Located at Apache Point Observatory in the mountains above Alamogordo, the Sloan is in the first year of a five-year project to map the sky above the northern hemisphere in unprecedented detail.
It's a joint project of a consortium of nine universities and research labs in the United States, Japan and Germany. Fan discovered the first of the methane brown dwarfs by accident while looking for the tell-tale signs of quasars -- giant objects in the distant regions of the universe.
The faint red light from the methane brown dwarfs drew his attention because it looked similar to the light expected from a quasar. But when he began looking closely at the data, he realized the object had important differences that meant it must be a nearby object, tiny and faint. Scientists had expected objects like methane dwarfs might exist in space -- indeed, one was discovered in 1995 orbiting a star.
But no one knew whether methane dwarfs could fly solo. "We really didn't know whether these things would exist free-floating in space," Golimowski said.
How they got there remains a mystery. The scientists say they could have been formed adjacent to a star and then flung out of orbit by a gravitational slingshot. Or they could have formed by themselves in empty space from a cloud of gas that collapsed under its own weight.
The light the telescope sees from the object is a remnant of the heat created in its formation, like the fading glow of a fireplace ember. The scientists don't know how far away the overgrown planets are. But methane dwarfs give off very little light, and so the fact that they can be seen at all indicates they must not be far away.
Golimowski estimated that they're within 30 light-years of Earth, an area in our neighborhood of the galaxy that contains perhaps 300 of the stars nearest to us.
And because two have been found in just the small part of the sky already surveyed, it's likely that there are many more to be found, with the number likely similar to the number of stars in our neighborhood, Golimowski said.
Fan said the discoveries demonstrate the power of the new kind of astronomy embodied in the Sloan. Instead of pointing at a single object an astronomer wants to study closely, the Sloan is slowly making its way across the entire sky, sucking up data on millions of objects.
The scientists involved can then use computers to study the attributes of large numbers of objects, looking for oddballs like Fan's and Golimowski's methane dwarfs, and also a better understanding of how the universe works.
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