Hubble Spots Possible New Moons Around Pluto
Posted: Tue Nov 01, 2005 10:28 am
The Hubble Space Telescope has spotted two possible new moons around Pluto, the ninth planet in the Solar System.
If confirmed, it would bring Pluto's tally of satellites to three; Charon, the only known moon of Pluto, was discovered by astronomers in 1978.
Confirmation of two new moons would shed light on the evolution of the Kuiper Belt, the vast region containing icy objects beyond Neptune's orbit.
All the candidate moon seem to orbit Pluto in an anti-clockwise direction.
The candidate moons, given the provisional names S/2005 P1 and S/2005 P2, appear to be just 140km and 125km in diameter, respectively. By comparison, Charon's diameter is about 1,200 km.
Observations suggest they orbit Pluto at least twice the distance Charon does. P2 stays about 49,000km from the planet, P1 lies even further away at 65,000km.
Fainter objects
Hubble's Advanced Camera for Surveys instrument observed the two new candidate moons on 15 May.
"The new satellite candidates are roughly 5,000 times fainter than Pluto, but they really stood out in these Hubble images," said Max Mutchler of the Space Telescope Science Institute in Baltimore, and the first team member to identify the satellites.
Three days later, Hubble looked at Pluto again. The two objects were still there and appeared to be moving in orbit around Pluto.
"A re-examination of Hubble images taken on 14 June 2002 has essentially confirmed the presence of both P1 and P2 near the predicted locations based on the 2005 Hubble observations," added Marc Buie of the Lowell Observatory, in Flagstaff, Arizona, another member of the team.
The discovery would make Pluto the first Kuiper Belt object known to have more than one satellite.
The team behind the discovery plans to make follow-up observations in February to confirm the objects really are new moons of Pluto.
Only then can the International Astronomical Union, consider names for the candidate satellites.
The researchers also looked for other potential moons around Pluto.
"These Hubble images represent the most sensitive search yet for objects around Pluto," said Andrew Steffl of the Southwest Research Institute in Boulder, Colorado.
The artist's concept above shows the Pluto system from the surface of one of the candidate moons. The other members of the Pluto system are just above the moon's surface. Pluto is the large disk at center, right. Charon, the system's only confirmed moon, is the smaller disk to the right of Pluto. The other candidate moon is the bright dot on Pluto's far left.
The Hubble Space Telescope images above, taken by the Advanced Camera for Surveys, reveal Pluto, its large moon Charon, and the planet's two new candidate satellites. Between May 15 and May 18, 2005, Charon, and the potential moons, provisionally designated P1 and P2, all appear to rotate counterclockwise around Pluto.
P1 and P2 move less than Charon because they are farther from Pluto, and therefore would be orbiting at slower speeds. P1 and P2 are thousands of times less bright than Pluto and Charon. The enhanced-color images of Pluto (the brightest object) and Charon (to the right of Pluto) were constructed by combining short exposure images. The images of the new satellites were made from longer exposures.
In the short-exposure image (above left), taken June 11, 2002, the candidate moons cannot be seen. They do, however, appear in the middle and right-hand images. Longer exposure times were used to take these images. Pluto and Charon are overexposed in these images, causing the bright streaks or "blooms" that emerge vertically from them.
The candidate moons are not overexposed because they are thousands of times less bright than Pluto and Charon. In these unprocessed images, various optical artifacts of the Advanced Camera for Surveys system are visible, such as the radial spokes of light caused by the telescope's optics.
If confirmed, it would bring Pluto's tally of satellites to three; Charon, the only known moon of Pluto, was discovered by astronomers in 1978.
Confirmation of two new moons would shed light on the evolution of the Kuiper Belt, the vast region containing icy objects beyond Neptune's orbit.
All the candidate moon seem to orbit Pluto in an anti-clockwise direction.
The candidate moons, given the provisional names S/2005 P1 and S/2005 P2, appear to be just 140km and 125km in diameter, respectively. By comparison, Charon's diameter is about 1,200 km.
Observations suggest they orbit Pluto at least twice the distance Charon does. P2 stays about 49,000km from the planet, P1 lies even further away at 65,000km.
Fainter objects
Hubble's Advanced Camera for Surveys instrument observed the two new candidate moons on 15 May.
"The new satellite candidates are roughly 5,000 times fainter than Pluto, but they really stood out in these Hubble images," said Max Mutchler of the Space Telescope Science Institute in Baltimore, and the first team member to identify the satellites.
Three days later, Hubble looked at Pluto again. The two objects were still there and appeared to be moving in orbit around Pluto.
"A re-examination of Hubble images taken on 14 June 2002 has essentially confirmed the presence of both P1 and P2 near the predicted locations based on the 2005 Hubble observations," added Marc Buie of the Lowell Observatory, in Flagstaff, Arizona, another member of the team.
The discovery would make Pluto the first Kuiper Belt object known to have more than one satellite.
The team behind the discovery plans to make follow-up observations in February to confirm the objects really are new moons of Pluto.
Only then can the International Astronomical Union, consider names for the candidate satellites.
The researchers also looked for other potential moons around Pluto.
"These Hubble images represent the most sensitive search yet for objects around Pluto," said Andrew Steffl of the Southwest Research Institute in Boulder, Colorado.
The artist's concept above shows the Pluto system from the surface of one of the candidate moons. The other members of the Pluto system are just above the moon's surface. Pluto is the large disk at center, right. Charon, the system's only confirmed moon, is the smaller disk to the right of Pluto. The other candidate moon is the bright dot on Pluto's far left.
The Hubble Space Telescope images above, taken by the Advanced Camera for Surveys, reveal Pluto, its large moon Charon, and the planet's two new candidate satellites. Between May 15 and May 18, 2005, Charon, and the potential moons, provisionally designated P1 and P2, all appear to rotate counterclockwise around Pluto.
P1 and P2 move less than Charon because they are farther from Pluto, and therefore would be orbiting at slower speeds. P1 and P2 are thousands of times less bright than Pluto and Charon. The enhanced-color images of Pluto (the brightest object) and Charon (to the right of Pluto) were constructed by combining short exposure images. The images of the new satellites were made from longer exposures.
In the short-exposure image (above left), taken June 11, 2002, the candidate moons cannot be seen. They do, however, appear in the middle and right-hand images. Longer exposure times were used to take these images. Pluto and Charon are overexposed in these images, causing the bright streaks or "blooms" that emerge vertically from them.
The candidate moons are not overexposed because they are thousands of times less bright than Pluto and Charon. In these unprocessed images, various optical artifacts of the Advanced Camera for Surveys system are visible, such as the radial spokes of light caused by the telescope's optics.