Post by Rose on Jun 16, 2006 16:20:06 GMT -5
www.abc.net.au/science/news/stories/s1576661.htm
Pluto really has two more moons
The tiny, distant and frozen planet Pluto, for 30 years believed to have just one moon, has two more satellites, US astronomers confirm.
They tentatively announced the discovery of the two moons last November.
Now they've confirmed their find, after spending six months analysing images from the Hubble Space Telescope and publishing their work in today's issue of the journal Nature.
Pluto's first known satellite Charon was not discovered until 1978. With a diameter of 1200 kilometres, it is half that of Pluto, abnormally large for a moon in relation to its planet.
Some scientists suspected Pluto had other, tiny moons. But at such a great distance from Earth, they have been hard to spot.
The two additional orbiting satellites, P1 and P2, are travelling outside the orbit of Charon and are tiny by comparison, say scientists led by Dr Hal Weaver of Johns Hopkins University.
P1, the more distant of the two from Pluto, has a diameter of between 60 and 165 kilometres while P2 is 20% smaller.
"Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon with orbital periods of about 38 days for P1 and 25 days for P2," they write.
Charon's density is also very similar to that of Pluto's, which appears to back theories that the planet whacked into a large space object, causing a large chunk to break off and eventually be enslaved as a satellite.
P1 and P2 may have resulted from the same collision, says Dr Alan Stern of the Southwest Research Institute in the same issue of Nature.
First with multiple satellites
The discovery of the two new members of Pluto's family make it the only object in the Kuiper belt, a vast region of rock and ice beyond Neptune that contains debris from the formation of the solar system, known to have multiple satellites, the scientists say.
The scientists also expect Pluto's small moons to generate debris rings of their own, from surface impacts.
"[This] would open up a whole new class of study because it would constitute the first ring system seen around a solid body rather than a gas giant planet," says Stern's colleague and co-author Dr Bill Merline.
Pluto was only discovered in 1930 and because of its vast distance from Earth has remained largely enigmatic ever since.
It's some three billion miles from the Sun and the only planet not yet to have been visited by a spacecraft.
NASA's New Horizons mission, which was launched earlier this year, will be the first to take a detailed look at Pluto, in 2015, and the Kuiper belt by 2020.
Pluto really has two more moons
The tiny, distant and frozen planet Pluto, for 30 years believed to have just one moon, has two more satellites, US astronomers confirm.
They tentatively announced the discovery of the two moons last November.
Now they've confirmed their find, after spending six months analysing images from the Hubble Space Telescope and publishing their work in today's issue of the journal Nature.
Pluto's first known satellite Charon was not discovered until 1978. With a diameter of 1200 kilometres, it is half that of Pluto, abnormally large for a moon in relation to its planet.
Some scientists suspected Pluto had other, tiny moons. But at such a great distance from Earth, they have been hard to spot.
The two additional orbiting satellites, P1 and P2, are travelling outside the orbit of Charon and are tiny by comparison, say scientists led by Dr Hal Weaver of Johns Hopkins University.
P1, the more distant of the two from Pluto, has a diameter of between 60 and 165 kilometres while P2 is 20% smaller.
"Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon with orbital periods of about 38 days for P1 and 25 days for P2," they write.
Charon's density is also very similar to that of Pluto's, which appears to back theories that the planet whacked into a large space object, causing a large chunk to break off and eventually be enslaved as a satellite.
P1 and P2 may have resulted from the same collision, says Dr Alan Stern of the Southwest Research Institute in the same issue of Nature.
First with multiple satellites
The discovery of the two new members of Pluto's family make it the only object in the Kuiper belt, a vast region of rock and ice beyond Neptune that contains debris from the formation of the solar system, known to have multiple satellites, the scientists say.
The scientists also expect Pluto's small moons to generate debris rings of their own, from surface impacts.
"[This] would open up a whole new class of study because it would constitute the first ring system seen around a solid body rather than a gas giant planet," says Stern's colleague and co-author Dr Bill Merline.
Pluto was only discovered in 1930 and because of its vast distance from Earth has remained largely enigmatic ever since.
It's some three billion miles from the Sun and the only planet not yet to have been visited by a spacecraft.
NASA's New Horizons mission, which was launched earlier this year, will be the first to take a detailed look at Pluto, in 2015, and the Kuiper belt by 2020.