May 11, 2016

Yesterday, May 10, we met over a thousand of Earth’s neighbors for the first time. Princeton University researcher Timothy Morton and a team of other scientists analyzed data returned by the U.S. National Aeronautics and Space Administration (NASA) satellite Kepler and detected over 1,200 more planets orbiting other stars, nearly double the amount previously known. The group announced the discoveries in a NASA press conference and published their results in The Astrophysical Journal.

The space telescope Kepler (Credit: NASA/Kepler mission/Wendy Stenzel)

Kepler is a space-based telescope originally designed to search for Earth-sized planets orbiting sunlike stars. Scientists refer to planets beyond our solar system as extrasolar planets or exoplanets. The telescope watched many stars simultaneously for small changes in brightness that might be caused by a passing planet. Kepler’s main goal was to find small, rocky planets—called terrestrial (Earthlike) planets—that orbit within their star’s habitable zone. In this region, temperatures allow for the existence of liquid water, which many scientists think is essential for life. The mission also helped scientists understand the variety of planetary systems that exist around sunlike stars. Kepler still hunts for planets today, albeit with a modified mission due to hardware failure on the craft.

Morton and his team developed a method to statistically analyze the likelihood that a promising return from Kepler could be caused by something other than an exoplanet, such as another star. If the probability of such a false positive was less than 1 percent, then the team reasoned that the result came from an exoplanet. Rather than use new observations, the team looked at over 4,000 objects of interest previously identified by the telescope. Of those objects, 1,284 were confirmed to be exoplanets (not counting the 984 already confirmed by other methods) and 428 were deemed false positives.

The new method will likely revolutionize the search for exoplanets. Before this study, astronomers have had to manually confirm all promising results returned by Kepler using Earth-based observatories, an expensive, time-consuming process. Now, they can use the Morton team’s method as a first pass, automatically confirming the most likely signals as exoplanets and ruling out the least likely ones. They can then spend their valuable research time on determining whether the trickier signals were caused by orbiting exoplanets.

Of the 1,200 newly discovered exoplanets, over 500 could potentially be rocky planets like Earth and Mars. Of these, nine orbit in their star’s habitable zone. In the future, astronomers will use even more powerful telescopes to study these exoplanets to try to answer one of astronomy’s greatest questions: are we alone in the universe, or is there other life out there?

October 17, 2012

Amateur astronomers have discovered an extraordinary planet–one whose skies are illuminated by four suns. The planet, whose discovery was announced this week at an astronomical conference in Reno, Nevada, was named Planet Hunters 1 (PH1). The name refers to the group of volunteers who study data from the Kepler space telescope that NASA has made available to the public on its Planethunters.org website. Two of those volunteers made the discovery, which was confirmed by professional astronomers.

PH1 is located about 5,000 light-years from Earth. (A light-year is the distance light travels in a year, about 5.88 trillion miles or 9.46 trillion kilometers.) Astronomers believe it is a gas giant, larger than Neptune but smaller than Saturn–about six times as wide as Earth. The planet orbits two of the four stars, circling the pair every 138 days. The two stars orbit each other every 20 days.

The other two stars in the system orbit the first pair, but they are located much farther away from the planet–about 93 billion miles (155 billion kilometers). Those other two stars shine in PH1′s sky at certain times of the year, sometimes at night and sometimes during the day.

Extrasolar planets orbit stars other than the sun. In this infrared image of the star HR 8799, three planets orbit the star. The arrows indicate the directions of the planets’ orbits. (C. Marois et. al/NCR Canada)

Two stars that orbit each other are called binary stars. Many of the stars in our solar system belong to such binary systems. Less common are planets that orbit binary stars. Of the hundreds of exoplanets (planets outside of the solar system) discovered so far, only six have been confirmed to orbit binary stars. PH1 is even rarer yet. It is the only planet ever discovered as part of a quadruple star system.

Additional World Book articles:

• Astronomy
• Kepler, Johannes
• Star
• Telescope
• Astronomy 2011 (Back in Time article)
• Space exploration 2009 (Back in Time article)

June 4, 2012

Venus will make a rare and historic journey across the face of the sun this week, an event that people alive today will almost certainly never have another chance to see. That journey, called a transit, will mark Venus’s passage between Earth and the sun, an astronomical event that comes along only about every 110 years. During the transit, Venus will appear as a dark dot moving across the sun’s disk. The transit can be seen on June 5 in much of the Western Hemisphere and on June 6 in a large part of the Eastern Hemisphere. Transits of Venus happen in pairs about eight years apart. The first of the current pair was in 2004. The previous transit occurred in 1882; the next won’t occur until December 10-11, 2117.

Venus appears as a dark dot moving across the sun's disk during a transit. Venus transits occur in pairs in which one transit happens 8 years after the other. (Jay M. Pasachoff, et al., Williams College Transit of Venus Team with John Seiradakis, et al., Aristotelian University, Thessaloniki, Greece)

A transit of Venus is an amazing astronomical display–and much more. While trying to determine how the planets move around the sun, the great German astronomer and mathematician Johannes Kepler became the first to predict a transit of Venus. But he died soon before the transit and no record of that event exists. However, the English astronomers Jeremiah Horrock and William Crabtree recorded the 1639 event.

In 1716, the English astronomer Edmond Halley proposed that the transit of Venus could be used to determine the distance between Earth and the sun. He suggested that by measuring the duration and time of the transit from many different locations, scientists could triangulate that distance. Unfortunately, measurements made during the next transit, in 1761, were insufficient.

Fortunately, the transit eight years later sparked a worldwide interest in the project. Scientists and other interested people scattered to the far reaches of the globe to gather the needed information. Among the observers was the English explorer James Cook. On orders from the Royal Navy, he traveled to the South Pacific island of Tahiti to make the observations. All the data gathered during the transit enabled scientists to calculate that Earth was 95 million miles (153 million kilometers) from the sun (very close to the actual distance of about 93 million miles [150 million kilometers]).

Scientists plan to use the 2012 transit to help in the search for extrasolar planets. Since 2009, NASA’s Kepler space telescope has been watching for small changes in the brightness of alien stars caused by the transit of an orbiting planet. By analyzing the starlight passing through the extrasolar planet’s atmosphere during the transit, scientists can learn about the chemicals in its atmosphere. During the transit of Venus, scientists will be studying Venus’s atmosphere with the Hubble Space Telescope. Although that planet’s atmosphere is already well understood, the information may help them determine the composition of extrasolar atmospheres.

Here are a few ways to view the transit safely. WARNING: NEVER LOOK DIRECTLY AT THE SUN.
1)    Wear solar eclipse shades, also called “solar filters,” which can be found online and in some science stores. Welders goggles rated “14″ or higher will also protect your eyes.
2)    Make a pinhole projector. Use two pieces of cardboard; punch a small hole in one of them. Hold this piece up to the sun so that sunlight passes through the hole and casts an image on the other piece.
3)    Use a telescope as a projector. You can do this by pointing the telescope at the sun and then projecting the image in the eyepiece onto any nearby flat surface, such as a wall or a piece of cardboard or paper. You can also use a pair of binoculars. Use only one side and cover the other side. (You could use both sides to make two images.)
4)    Watch the live webcast from atop Mauna Kea in Hawaii sponsored by NASA EDGE: http://sunearthday.nasa.gov/2012/transit/webcast.php.

Additional World Book articles:

• Space exploration (Probes to Venus and Mercury)
• Spectrometer
• In Search of Other Worlds (a Special Report)

Jan. 13, 2012

Planets orbiting stars other than the sun may be the rule rather the exception, an international team of scientists has reported. In fact, the Milky Way alone–an average-sized galaxy among the billions of galaxies in the universe–probably contains at least 160 billion planets. And even that, the scientists said, is a conservative estimate.

The scientists reached that number after making a statistical analysis of planets found using gravitational lensing, one of the main methods for hunting for extrasolar planets. They calculated that each star in the Milky Way has an average of 1.6 planets. Then they multiplied this number by the 100 billion stars estimated to belong to the Milky Way. Gravitational lensing, however, is not useful for finding exoplanets less than five times larger than Earth. Nor is it especially useful for finding planets that orbit closer to their star than Venus or farther from their star than Saturn. So the total number of alien planets is certainly much higher.

Three rocky planets smaller than Earth--the first alien planets that small found outside the solar system--have been found orbiting a red dwarf about 120 light-years from Earth. The smallest of the three planets (foreground), which is about the size of Mars, actually orbits the farthest from the star. NASA/JPL-Caltech

Evidence for that conclusion was the discovery of the first exoplanets smaller than Earth outside the solar system. Astronomers studying data imaged by the Kepler space telescope found the three rocky planets about 120 light-years from Earth. One of the planets is about the size of Mars, about half the size of Earth. All three orbit so close to their star, a red dwarf, that their sizzling surface temperatures rule out the existence of life as we know it. The Kepler scientists said the galaxy might have many more small planets than it has large planets. Astronomer John Johnson, one of the authors of the study, said that small exoplanets were “kind of like cockroaches. If you see one, then there are dozens hiding.”

Additional World Book articles:

• Back in Time (Astronomy 1996)
• Back in Time (Astronomy 1999)
• COROT
• In Search of Other Worlds (A Special Report)
• Kepler, Johannes
• Transit

Dec. 21, 2011

The Kepler space telescope has spotted two Earth-sized planets orbiting a star about 1,000 light-years from Earth. The two planets are the smallest yet found orbiting a sun-like star. The smaller of the planets, named Kepler-20e, is about 0.87 times as large as Earth–about the size of Venus. Kepler-20e is the first extrasolar planet smaller than Earth to be discovered. The other, named Kepler-20f, is 1.03 times as large as Earth–slightly larger than Earth. Astronomers believe that the two planets orbit too close to the star to support life. The surface temperatures were reported to be about 800 °F (426 °C) on Kepler-20f and about 1,400 °F (760 °C) on Kepler-20e.

Kepler-20e is the first planet smaller than Earth to be discovered outside the solar system. It orbits its star in only six days. NASA/Ames/JPL-Caltech

The Kepler telescope was launched in March 2009. Its main mission is to search one section of our 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. Earlier in December, the Kepler team announced the discovery of the first confirmed Earth-like planet in the habitable zone of another star. Scientists believe this planet is too large to have a solid rocky surface.

Although the three planets may not support life, the discoveries mark important steps in Kepler’s mission. Kepler’s ultimate goal is to spot a planet of similar size and temperature as Earth. At that point, scientists can study the planet with other instruments and techniques to determine if the planet does indeed have liquid water and, possibly, indications of life.

Additional World Book articles:

• COROT
• Kepler, Johannes
• Planet (Planets in other solar systems)
• Transit

The United States government has no knowledge that extraterrestrial life exists or that beings from other planets have made contact with humans, according to a formal statement issued by the White House Office of Science and Technology Policy. In the statement, space policy expert Phil Larson declared, “The U.S. government has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race. In addition, there is no credible information to suggest that any evidence is being hidden from the public’s eye.”

Some people believe UFO's are spaceships from other planets. However, investigators discover ordinary explanations for most UFO sightings. © Popperfoto/Alamy Images

The announcement was made in response to two online petitions addressed to “We The People,” a government website that promises to address issues raised by any petition with at least 5,000 signers. The petitions asked the administration of President Barack Obama for any government knowledge of contact with extraterrestrials (ET’s). One of the petitions insisted that, “The people have a right to know. The people can handle the truth.” Many people throughout the world believe that some unidentified flying objects (UFO’s) are spacecraft from other planets. Some people have even reported being abducted by aliens.

Larson acknowledged that the U.S. government has engaged in several projects to search for extraterrestrial life. In 2009, NASA launched Kepler, a space-based telescope designed to search for Earth-sized planets orbiting sun-like stars.  The SETI Institute in California also scans the universe for signs of intelligent life. In November, NASA planned to launch a new Mars rover named Curiosity. It is designed to search for evidence that Mars has had elements that could support microbial life. In 1952, the U.S. Air Force established Project Blue Book, a program to investigate about 12,000 UFO reports to determine whether UFO’s were a potential threat to national security. The project was cancelled in 1969, after scientists at the University of Colorado advised the Air Force that further study was not likely to produce useful information concerning a security threat.

Additional World Book articles:

• Area 51
• Roswell

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