LONDON—The tiny, distant and frozen planet Pluto, for 30 years believed to have just one moon, has suddenly been found to have two more satellites.
Only discovered in 1930 because of its vast distance from Earth, Pluto has remained a largely mysterious object ever since.
Some three billion miles from the Sun, Pluto, a dwarf planet, remains to be visited by a spacecraft.
Its first known satellite is called Charon. With a diameter of 1,200 km, it is half that of Pluto—unusually large for a moon in relation to its primary.
But now, using images from the Hubble Space Telescope, scientists from Johns Hopkins University, Southwest Research Institute and the Massachusetts Institute of Technology say they have found two more tiny orbiting satellites, P1 and P2.
Both are traveling outside the orbit of Charon and are tiny by comparison, the scientists wrote in the journal Nature.
P1, the more distant of the two from Pluto, has a diameter of between 60 and 165 km while P2 is 20 percent smaller.
"Although definitive orbits cannot be obtained, 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 wrote.
The discovery of the two new members of Pluto's family makes it the only object in the Kuiper belt—a vast region of rock and ice beyond Neptune which contains debris from the formation of the solar system—known to have multiple satellites, the scientists said.
1. It is implied in the passage that______.
A. Charon was not discovered until the late 1960s
B. Charon is the largest satellite in the solar system
C. all the inner planets are better observed than Pluto
D. Pluto may have some more moons to be discovered
2. The underlined word "primary" in Paragraph 4 refers to______.
A. size B. shape C. planet D. Earth
3. Which of the following show the possible orbits and positions of Pluto's satellites?
A B C D
4. Which of the following is the best title for the passage?
A. Pluto: furthest in the solar system.
B. Pluto: two additional moons found.
C. Pluto: tiny, distant and frozen planet.
D. Pluto: two satellites formed in 30 years.