WASHINGTON – The Hubble Space Telescope has discovered a fourth moon orbiting the distant icy dwarf planet Pluto, Nasa said yesterday.
The space telescope was searching for rings around the planet at the edge of our solar system when it came across P4, the temporary name for the discovered moon.
With an estimated diameter of 13km to 34km, P4 is the smallest of Pluto’s four moons, the US space agency said in a statement.
Pluto’s largest moon, Charon, is 1,043km across and its other moons, Nix and Hydra, are in the range of 32 to 113km in diameter.
“I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 5 billion kilometres,” said Mark Showalter of the SETI Institute in Mountain View, California, who led this observing programme with Hubble.
The observation by Hubble is part of ongoing work to support Nasa’s new horizons mission, scheduled to have a close encounter with Pluto and its moons in 2015.
P4 is located between the orbits of Nix and Hydra, both of which were discovered by Hubble in 2005.
Charon was discovered in 1978 at the US Naval Observatory.
All four of Pluto’s moons are believed to have formed when Pluto and another planet-sized body collided in the early history of our solar system.
The Earth’s moon may have formed the same way.
P4 was first seen in a photo taken by Hubble on June 28th and was confirmed in subsequent Hubble pictures taken on July 3rd and July 18th, Nasa said.
In June, Pluto came between a star and Earth, casting a small shadow on Earth’s surface that astronomers tracked across the Pacific.
This event, known as an occultation, occurred on June 23rd, scientists at Lowell Observatory in Arizona said.
Four of them travelled on a modified 747 aircraft that carried a big telescope, which managed to take images of Pluto and its thin atmosphere.
Learning more about Pluto’s tenuous atmosphere is possible because the starlight behind it dims in a specific way, which lets astronomers determine atmospheric temperature and density, Lowell Observatory said yesterday.
Pluto cast an extremely long shadow, it has an average distance of 9.495 billion kilometres from the sun, compared to Earth’s distance of 149.7 million kilometres. – (Reuters)