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)

June 20, 2013

Kepler space telescope has turned up another 503 potential exoplanets, mission control officials at NASA‘s Ames Research Center in Moffett Field, California, announced recently. This brings to 3,216 the number of planet candidates detected by the orbiting probe since its launch in March 2009. Further investigation has confirmed that 132 of those objects are, in fact, extrasolar planets.

Unfortunately, Kepler’s planet-hunting days may be over. Since mid-May, Kepler has been nonoperational because of an equipment malfunction. At that time, mission controllers discovered that one of the craft’s reaction wheels was not working. These devices keep the craft aimed precisely in the right direction. Kepler, which needs three reaction wheels to operate properly, now has only two. Originally, the telescope carried a spare, but that device was put into service when another of the reaction wheels quit working in 2012.

A planet about the size of Saturn, known as Kepler-35b, orbits a binary star (pair of stars) in an artist's illustration of a planetary system discovered by Kepler.

Kepler’s main mission is to search one section of the Milky Way Galaxy for Earth-like planets in the “habitable zone.” The habitable zone, also called the Goldilocks zone, is the region around a star that scientists believe is neither too hot nor too cold to support life as we know it. In this zone, the temperature is cool enough to let liquid water form and warm enough to prevent water from freezing. Earth orbits in the habitable zone of the solar system. Kepler has searched over 150,000 stars for signs of orbiting planets.

Additional World Book articles:

• Binary star
• Planet
• In Search of Other Worlds (a special report)
• Space exploration (2011) (a Back in Time article)

March 27, 2012

Sometimes things are not as simple as they appear. Take the planet Mercury, for instance. In a very short time, the smallest planet in the solar system (sorry Pluto, you’re no longer a planet) has gone from a simple hunk of rock, much like Earth’s moon, to one of the most unusual planets ever studied. For years, most astronomers thought that Mercury formed early in the solar system’s history and has since remained pretty much unchanged. New evidence shows a planet whose more recent history includes active volcanoes, a shifting crust, and other activities once thought to have ended billions of years ago. Some of these activities may result from the fact that Mercury is slowly shrinking. The shrinking would explain why the outer layer of the planet is buckling and cracking. A closer look at the surface also shows evidence of lava flows having occurred much more recently than previously thought.

The MESSENGER space probe has revealed surprising new findings about the smallest planet in the solar system. (Courtesy of NASA)

The planet’s surface is not the only surprise. Mercury may also have an internal structure like no other planet yet studied by scientists. Mercury appears to have a core consisting of three layers. Earth has only two such inner layers. Both Mercury and Earth have an inner core of solid metal surrounded by a second layer of liquid metal. Unlike Earth, Mercury appears to have a third layer made of solid iron and sulfur. Many scientists now speculate that this possible third layer of core explains one of the great mysteries concerning Mercury. Scientists have long wondered how the planet could be so small and yet have a much greater mass than the other inner planets–Venus, Earth, and Mars–for its size.

The new data on Mercury was collected by the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) space probe. Launched in 2004 by NASA, MESSENGER began a one-year mission orbiting Mercury in early 2011 (which NASA scientists have now extended). The probe reached the planet after a more than five-year tour of the inner solar system. The long, looping route involved three close fly-bys of Mercury along with close approaches to Venus and Earth.

Just how loopy was the route MESSENGER took? Mercury is only about 20 percent farther from Earth than Mars when those planets pass closest to Earth. Yet, a probe going to Mars travels for less than a year. By comparison, MESSENGER took more than five years to reach Mercury.

Additional World Book articles

• Probing the Planets (a special report)
• Space Exploration 2004 (Back in Time article)
• Space Exploration 2008 (Back in Time article)
• Space Exploration 2009 (Back in Time article)
• Space Exploration 2011 (Back in Time article)

Nov. 2, 2011

The dwarf planet Eris, whose discovery in 2005 contributed to Pluto’s demotion from planet to dwarf planet, is actually a bit smaller than Pluto, new observations suggest. Discovered in 1930, Pluto was widely considered a full-fledged planet­, until scientists found Eris. At first, it seemed that Eris, which appeared to be slightly larger than Pluto, might become the 10^th planet. Instead, the possibility that astronomers might find many more objects about the size of Pluto and Eris led to a scientific debate about the definition of a planet. In 2006, the International Astronomical Union, the body in charge of naming objects in space, created a formal definition for a planet as well as a new category of objects called dwarf planet for Eris and Pluto.

Eris, Pluto, and two other dwarf planets, called Makemake and Haumea, are found in the Kuiper belt, the area of the solar system immediately beyond the orbit of Neptune. A fifth dwarf planet called Ceres is the largest member of the Main Belt, a region of asteroids between the orbits of Mars and Jupiter. The new observations indicate that Eris is less than 1,454 miles (2,340 kilometers) in diameter. Pluto is about 1,455 miles (2,342 kilometers) wide. All the dwarf planets are smaller than Earth’s moon. Some scientists think there may be thousands of dwarf planets in the solar system.

This illustration shows the dwarf planets Ceres, Eris, Haumea, Makemake, and Pluto and their moons in comparative size to Earth and the moon. UCAR/University of Michigan.

Despite their similar size, Eris and Pluto are remarkably different. Eris is much denser and shinier than Pluto. In fact, Eris is one of the brightest objects in the solar system. Scientists think Eris may be so shiny because of methane ice on its surface.

Additional World Book articles:

• Back in Time (Astronomy,  1930)
• Back in Time (Astronomy, 2005)
• Exploring the Suburban Solar System (special report)
• Tombaugh, Clyde William

The discovery of a planet that orbits two stars-an arrangement that some scientists previously thought existed only in science fiction-was announced by astronomers at NASA‘s Ames Research Center in Mountain View, California. Kepler space telescope detected the planet, which scientists named Kepler-16b. The research team uses data from the telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets. (A transiting planet is a celestial body that moves across the face of another celestial body, hiding a small part of it.) Kepler-16b is about 200 light years from Earth and about the size of Saturn. Astronomers believe that Kepler-16b is gaseous and too cold to harbor life. It orbits the two stars in 229 days. The stars in turn circle each other.

“This discovery confirms a new class of planetary systems that could harbor life,” notes Kepler astronomer William Borucki. “Given that most stars in our galaxy are part of a binary (two star) system, this means the opportunities for life are much broader than if planets form only around single stars. This milestone discovery confirms a theory that scientists have had for decades but could not prove until now.”

Additional World Book articles:

• Astronomy
• Kepler, Johannes
• Hubble Space Telescope

Dark streaks running down the walls of several craters on Mars may be evidence of water flowing across the surface of the red planet during the Martian spring and summer. The discovery of the streaks, in images taken by NASA’s Mars Reconnaissance Orbiter, was reported by scientists at the University of Arizona. Since the mid-1900′s, scientists have gathered a great deal of evidence suggesting that water flowed over the Martian surface in the distant past.

Channels on Mars (NASA)

The finger-like streaks, which ranged from 1.6 to 16 feet (0.5 to 4.8 meters) wide, were seen in seven craters in various parts of Mars. All were on steep slopes facing the equator. Observed over three Martian years, the streaks appeared in late spring, grew and shifted during the summer, and disappeared in the fall. Some of the streaks grew as much as 600 feet (183 meters) over two Earth months.

The Arizona scientists said that though the streaks may have been caused by frozen carbon dioxide or even rock slides, their best explanation is salty water. However, they noted that they would not be able to confirm that water created the streaks without actually testing samples of the soil in the craters.

The scientists said that the surface of Mars is so salty that any water flowing there would certainly also be salty. The salty nature of the water may help explain its existence on the surface. Salt lowers the freezing point of water, so it can remain a liquid at temperatures colder than 32 °F (0 °C). The scientists doubted that life could exist in such a salty liquid.

Additional World Book articles:

• Astrobiology
• Extremophile
• Space exploration
• Astronomy 2008 (Back in Time article)
• Space exploration 2005 (Back in Time article)
• Space exploration 2006 (Back in Time article)