Every day, we experience the friendly embrace of gravity. The force of mutual attraction keeps the planets in orbit around the Sun, attaches us firmly to the Earth, and annoys us when we drop something on the floor. But gravity has some other interesting properties. According to Einstein's theory of general relativity, massive objects warp space and time. The force of gravity can cause light to bend toward an object like a giant galaxy. We can watch this happen in an effect called "gravitational lensing," when the gravity of a massive object, like a galaxy, warps and magnifies the images of more distant objects -- much like a giant lens in space. Scientists have found quite a few of these lenses using the Sloan Digital Sky Survey and the Hubble Space Telescope. In fact, 19 new "gravitationally lensed" galaxies have been added to the list of 100 already known. Eight of the objects are so-called "Einstein rings" - beautiful rings produced when two galaxies are almost perfectly aligned.
So what does it take to be a planet? Astronomers using the Hubble Space Telescope have noticed that Ceres, the largest of the asteroids circling the Sun, may contain large amounts of water ice frozen beneath its surface. Ceres is already odd because it's round like a planet, not potato-shaped like most asteroids. Its roundness suggests that its interior likely has a rocky inner core with dense materials, and a thin, dusty and lighter outer crust. Rocky planets like Earth and Mars have a similar structure. So Ceres could be an embryonic planet. It might have formed into a larger sphere if gravity from nearby Jupiter hadn't prevented more material from falling onto Ceres billions of years ago. A new NASA mission called Dawn will launch in 2006 to orbit Ceres and take the first close-up look at the asteroid. Dawn will also visit Vesta, the solar system's second largest asteroid.
For 35 years, the origin of the powerful, split-second flashes of light known as short gamma-ray bursts has been a mystery. Short gamma ray bursts are intense flashes, brighter than a billion suns, that last only a few milliseconds. They're difficult to study because they happen so quickly, without warning, anywhere in the sky. Catching one is like being in a crowd and having a camera flash go off behind your back. You can't turn fast enough to detect where the flash came from. Two years ago, scientists discovered long gamma ray bursts, lasting more than two seconds, that arise from the explosion of massive stars. But about 30 percent of gamma ray bursts are shorter than that. Observations by a number of satellites have helped resolve this puzzle. The recently launched Swift satellite detected a short burst on May 9, 2005, and the Chandra X-Ray Observatory observed -- for the first time ever -- its afterglow. NASA's High-Energy Transient Explorer detected another burst on July 9, 2005. The burst and afterglow suggest a violent collision. Scientists now believe that short gamma ray bursts result from collisions between either a black hole and a neutron star or two neutron stars. In either scenario, the impact creates a new black hole, releasing a terrific amount of energy.
Everyone asks whether the Sun is shining. Hans Bethe asked why it was shining. Bethe, who died in March 2005 at age 98, was the first to explain how the Sun generates energy to shine. In the 1920s, when Bethe was first studying physics, scientists knew that the Sun could release energy by contracting gravitationally. But such shrinking does not produce enough energy to account for the Sun's output. In the late 1930s, Bethe and fellow scientist Charles Critchfield demonstrated how a sequence of nuclear reactions could make the Sun shine. He won the Nobel Prize in 1967 for solving this puzzle and others involving energy production in stars. Bethe was borne on July 2, 1906, in Strasbourg, Germany. He exhibited an early interest in numbers and could do square roots at age 4, and fractions and most other math functions by the age of 5. He fled Europe for America in 1935 under the shadow of Nazism, and joined Cornell University. He worked on the atomic bomb, but became a champion of arms control after World War II. He continued to study stars and the Sun, focusing on supernovae and the high energy physics. Near the end of his long life, at age 95, he saw his theories about solar particles called neutrinos confirmed by difficult, precise measurements made possible with new technology.
This newest image of Pluto - our most distant planetary neighbor - shows more detail than any taken before. It might not look like much, but keep in mind that Pluto is only 1,400 miles (2,253 km) across - about two-thirds the size of our Moon - and more than 3.5 billion miles (5.6 billion km) away. It took the Hubble Space Telescope a dozen orbits around the Earth for the Hubble Space Telescope to take the picture, and nearly two years of computer processing to stitch all the information together. The image shows most of the spherical surface of Pluto spread out into a flat map. The red areas indicate methane ice, which seems to be everywhere. The dark areas may be dirty water-ice. Lighter areas indicate nitrogen frost. The bright spot near the center of the map could be a sign of carbon monoxide. NASA's New Horizons spacecraft is slated to launch in February 2006 on a mission to Pluto - the only planet never visited by spacecraft. It will take close to 10 years to reach the cold planet. After its arrival in 2015, New Horizons will travel on to investigate Pluto's cousins, the icy bodies known as Kuiper Belt Objects. Many contend that Pluto itself should be classified as a Kuiper Belt Object, not a planet.
Check out the night sky soon for a great view of Mars. The "Red Planet" is putting in its brightest appearance until the summer of 2018. You don't need a telescope - just look for a dazzling, star-like object that doesn't twinkle. Mars and Earth have been slowly approaching each other over the past months as they orbit the Sun, and Mars has been getting brighter as it gets closer. The two planetary neighbors will be 43,137,071 miles (69,422,386 km) apart at their closest on Oct. 29. That's still 180 times farther than the Moon, but less than half the distance to the Sun. Mars' orbit will bring it closer to Earth than any other planet except Venus. Another important date is Nov. 7, when Mars arrives at "opposition" to the Sun. As viewed from Earth, the Sun and Mars will be opposite each other in the sky. Mars will rise at sunset and set at sunrise, and therefore remain in the sky all night long. Happy Mars hunting!
Searching for tiny planets near bright stars is challenging. Astronomers would need incredibly large telescopes to detect small planets near host stars. Alternately, they can use several linked telescopes to detect the planets' faint signals. The telescopes work together as one to create the effect of a single giant telescope. The European Space Agency is planning an ambitious mission, called Darwin, that will fly several telescopes together in space. Sweden is interested in building a small, experimental satellite to test the idea. The satellite, Prisma, consists of a large telescope and a smaller second component, called a nano-satellite, that will work together to collect light from space. It could launch as early as 2008.
NASA's Deep Impact mission has given us our closest look at a comet nucleus, and achieved our first contact with one. The Deep Impact spacecraft ejected a robotic probe that collided with Comet Tempel 1 on July 4, 2005, causing a huge explosion. The impact smashed free a cloud of material that the nearby spacecraft observed. Scientists are now analyzing the data to determine the makeup of the comet. The old idea of comets being "dirty snowballs" may be changing to "snowy dirtballs," since Tempel 1 seems to contain more dust than ice. In fact, the comet may be "mostly empty," in the words of the mission's chief scientist, Dr. Michael A'Hearn from the University of Maryland. Scientists are also surprised by the number of craters on Comet Tempel 1's surface. Neither of the two comets spacecraft previously observed up close appeared to have any craters. Why would comets be so different? Comets are of great interest to scientists because the ice and other materials deep inside are likely pristine and unchanged from early days of solar system.
Astronomers are often asked to determine the time, date, and plausibility of events based on the appearance of the sky. Texas researchers have been investigating famous historical events, art, and literature by studying the astronomical configurations they can deduce were in force at the time. For example: Ansel Adams took the photograph entitled "Autumn Moon, the High Sierra from Glacier Point" some time in 1948 ? or was it another year, as some have argued? Donald Olson and Russell Doescher say no! It was actually Sept. 15, 1948, at 7:03 p.m. Pacific Daylight Time. This scene repeated itself this year at nearly the same time on September 15. An added bonus of the astronomers' investigation: a discovery of a color version Adams took while testing Kodak film.
It might be a lake, but you wouldn't want to vacation nearby. Titan, the largest of Saturn's 34 known moons, could have a lake of liquid methane on its surface. Titan, a moon bigger than the planets Mercury and Pluto, has its own atmosphere. NASA's Cassini mission, which has been orbiting Saturn for more than a year, sent out a probe, called Huygens, to Titan's surface. The probe sent images back as it descended. The images show a feature near Titan's south pole that looks like a lake of approximately 145 miles by 45 miles. It has a smooth shoreline and is reminiscent of Earth's lake shores. The region has methane clouds, so if the feature is a lake, it could have been formed by methane raining onto the surface. The next step is to see if the surface of the "lake" is liquid. Without landing there, how can researchers find this out? One idea is to search for reflections off of the surface of the feature, like the glare of sunlight from a water lake on Earth.
New studies of Martian meteorites that have landed on Earth suggest that Mars has been colder than freezing for an extremely long time. Detailed chemical analysis of the Mars meteorites, including the famous ALH84001 meteorite from Allan Hills in Antarctica, shows the long-term temperature of those rocks as very cold. During the last 4 billion years, Mars was likely never warm enough for water to flow on the surface for extended periods of time.