March 28, 2014

A probable dwarf planet that orbits much farther from the sun than any other known object has been discovered by American astronomers Chad Trujillo and Scott Sheppard. The little planet is so far away that its orbit takes it 15 times as far from the sun as the orbit of Neptune, the most distant major planet in the solar system. The astronomers first sighted the object, designated 2012 VP113, or VP for short, using the Dark Energy Camera mounted on the 4-meter Blanco telescope in Chile. However, to confirm the shape of the object’s orbit around the sun, the astronomers needed to watch the object for many months. The would-be dwarf planet VP is the second such object found orbiting the sun at such a vast distance. The first, named Sedna, was discovered in 2003 by a team that included Trujillo. VP appears to be about 280 miles (450 kilometers) across, about half the size of Sedna and the most commonly known dwarf planet, Pluto. Trujillo and Sheppard nicknamed the new dwarf planet Biden, for United States Vice President Joe Biden.

The distance from Earth to the sun is, on average, about 93 million miles (150 million kilometers). This distance is called an astronomical unit or AU. Neptune is about 30 AU from the sun. The orbit of Sedna is a stretched out oval that carries it as far as 1,000 AU from the sun. However, Sedna also comes to within 76 AU of the sun at its closest approach. The orbit of VP is more circular. For this reason, VP doesn’t stray as far as Sedna, only about 450 AU. On the other hand, VP never gets closer than 80 AU to the sun at its closest approach, farther than any other solar system body known.

Dwarf planets Ceres, Eris, Haumea, Makemake, and Pluto and their moons, compared with Earth and its moon. All of these dwarf planets are smaller than the moon. (©UCAR/University of Michigan)

The area to which Pluto and several other dwarf planets belong is called the Kuiper belt. It is the region beyond Neptune and includes millions of icy bodies. Far beyond the Kuiper belt is a region called the Oort cloud, an area thought to be filled with millions of comets. Both Sedna and VP orbit between the Kuiper belt and the Oort cloud. Many astronomers believed this area was empty. The discovery of Sedna and now VP puts that idea into question.

The discovery offers new information about how the solar system was formed. How did such large objects assume orbits so far from the sun? How many are there yet to be found? One interesting conclusion suggested by astronomers studying the new data is that the orbits of Sedna and VP may be influenced by a large, yet undiscovered planet.

Additional World Book articles:

• Ceres
• Eris
• Planet (the dwarf planets)
• Exploring the Suburban Solar System (a Special Report)
• Astronomy (2004) (a Back in Time article)
• Astronomy (2006) (a Back in Time article)

September 10, 2012

Bearing greetings from Earthlings now more than 11 billion miles (18 billion kilometers) away, the Voyager 1 spacecraft continued its epic trek to the edge of the solar system on September 5, 35 years after its launch into space. NASA had launched a companion craft, Voyager 2, on August 20, also in 1977. Together, the two probes have lasted longer and traveled farther than any other space probes in history. Voyager 2 is now about 9 billion miles (15 billion kilometers) from the sun, going south, the opposite direction from Voyager 1.

The space probe Voyager 2 was launched on Aug. 20, 1977. Its path through the solar system is shown in red. Voyager 2 flew past and photographed Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. (World Book illustration by Ken Tiessen, Koralik Associates)

Initially, the two spacecraft were given a five-year mission to explore the gas giants Jupiter and Saturn. The data they sent back to Earth have answered many questions about the planets’ atmospheres, interiors, rings, magnetospheres (surrounding zones of strong magnetic fields), and satellite systems. With this part of the Voyager mission completed, engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, in 1981 decided to push the two craft farther into space. Voyager 2 became the first–and so far–only spacecraft to visit Uranus and Neptune. They found evidence of geologic activity on two previously known moons—volcanoes on Jupiter’s moon Io and icy geysers on Neptune’s moon Triton.

Since 1989, the two probes have been exploring the heliosphere, a vast, tear-drop-shaped region of space that contains the solar system, the sun’s magnetic field, and the solar wind (electrically charged particles given off by the sun). In late 2004, Voyager 1 crossed a shock wave called the termination shock, becoming the first craft to reach the region of space that lies just inside the heliopause (the final boundary of the solar system). The crossing occurred at a distance of about 8.7 billion miles (14 billion kilometers) from the sun. In 2007, Voyager 2 crossed the shock in a different area and at a distance of about 7.8 billion miles (12.6 billion kilometers) from the sun. By detecting the shock at different distances from the sun, the two craft confirmed scientists’ belief that the solar system is not perfectly round.

The two Voyager spacecraft explore the outer edges of the heliosphere, a vast, tear-drop-shaped region of space that contains the solar system, in an artist’s illuustration. (NASA/JPL-Caltech)

Scientists are not sure when Voyager 1 and 2 will leave the heliosphere and go where no spacecraft has gone before–interstellar space. Some signals from Voyager 1 suggest that the craft’s escape from the solar system may occur in the near future. Regardless, the two spacecraft will have enough electrical power to continue collecting data and communicating it back to Earth through 2020, and possibly through 2025.

Additional World Book articles:

• Space exploration
• The Thirty-Year Journey of Voyagers 1 & 2 (A Special Report)
• Astronomy (1979) (A Back in Time article)
• Astronomy (1989) (A Back in Time article)
• Space Exploration (1977) (A Back in Time article)
• Space Exploration (1979) (A Back in Time article)