March 1, 2017

On February 22, astronomers announced the discovery of a remarkable planetary system orbiting a relatively nearby star. Planets outside the solar system are called extrasolar planets or exoplanets. The new system has a whopping seven planets, many of which might host conditions favorable for life. The finding was published in the journal Nature.

This artist’s concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances.
Credit: NASA/JPL-Caltech

The system is located some 40 light-years away in the constellation Aquarius, the Water Bearer. One light-year is the distance that light travels in a vacuum in a year, about 5.88 trillion miles (9.46 trillion kilometers). The planets orbit a star called TRAPPIST-1, named in honor of the telescope used in the discovery. TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope. It is a robotic telescope in Chile funded by Belgium. In May 2016, TRAPPIST detected three planets orbiting a type of small, relatively cool star called a red dwarf. In September, the Spitzer Space Telescope, operated by the United States National Aeronautics and Space Administration (NASA), began monitoring the system. With the help of NASA’s Hubble Space Telescope and other ground-based telescope systems, Spitzer confirmed the existence of two of the planets. But Spitzer determined that the third signal detected by TRAPPIST actually came from four planets, not one. Later, the telescope observed traces of a seventh, even more distant, exoplanet.

Even this farthest exoplanet orbits closer to TRAPPIST-1 than Mercury does to the sun, at a distance of only about 5.6 million miles (9.0 million kilometers). For comparison, Earth orbits about 93 million miles (150 million kilometers) from the sun. Because red dwarfs are much smaller and cooler than the sun, however, three of the planets orbit within a region that should be neither too hot nor too cold for liquid water to exist on their surfaces. Most scientists consider liquid water essential for life, so such a region around a star is known as its habitable zone.

The planetary system’s compact size would provide spectacular views only imagined in science fiction. The star TRAPPIST-1 would appear three times as large as the sun does on Earth, bathing the planets with a dim, pinkish light. Because the exoplanets are so close together, an observer standing on one planet could clearly see the other six. Neighboring planets would sometimes appear larger than does the moon in Earth’s sky.

Follow-up studies are already underway. NASA’s renowned planet-hunting satellite Kepler is currently examining the system. All seven planets are about the size of Earth, but Kepler will more precisely calculate their sizes and possibly find more planets. Spitzer has already confirmed that two of the planets are rocky worlds, rather than gaseous planets like Neptune. But Spitzer will continue to examine the system to learn more about the planets’ masses and compositions. In 2018, NASA plans to launch the James Webb Space Telescope. This powerful satellite should be able to detect if any of the exoplanets have atmospheres and determine their compositions. If the atmosphere contains compounds such as methane, oxygen, and ozone, it would be a strong indication that life exists there.

Other Behind the Headlines posts:

• Ten to 30 Alien Planets for Every Person on Earth? (Jan. 13, 2012)
• Amateur Astronomers Discover a Planet with Four Suns (Oct. 17, 2012)
• New Exoplanet Candidates from Ailing Kepler Spacecraft (June 20, 2013)
• Kepler Space Telescope Goes Dark–For Now (Aug. 16, 2013)
• Exoplanet Bonanza from Kepler (Feb. 27, 2014)
• First “Earth-Cousin” Found by Kepler Space Telescope (May 1, 2014)
• “Hello, Aliens? Are You Out There?” (Feb. 13, 2015)
• New Planetary Neighbors (May 11, 2016)
• The Pale Red Dot: Proxima b (Aug. 31, 2016)
  

May 1, 2014

The first Earthlike planet orbiting in the “Goldilocks zone” of a star other than the sun has been found by scientists analyzing data from the Kepler space telescope. The Goldilocks zone is the region around a star in which liquid water can exist. That is, the planet, called Kepler-186f, is not too hot to cause water to evaporate or too cold to cause it to freeze. Scientists believe the most likely place to find life as we know it is on planets or moons that can support liquid water.

“Being in the habitable zone does not mean we know this planet is habitable,” commented Thomas Barclay, a research scientist at the Bay Area Environmental Research Institute at Ames, and co-author of the paper. “The temperature on the planet is strongly dependent on what kind of atmosphere the planet has. Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth.”

The newly discovered extrasolar planet is just 10 percent larger than Earth. It orbits a type of star called a red dwarf. Smaller and cooler than the sun, red dwarfs are also the most abundant type of star in our galaxy, the Milky Way. The star, called Kepler-186, is about half the size and mass of the sun. It is about 500 light-years from Earth in the constellation Cygnus. Four other planets orbit Kepler-186.

Extrasolar planets orbit stars other than the sun. This infrared image of the star HR 8799 and its three orbiting planets was taken in 2008. The arrows indicate the directions of the planets’ orbits. (C. Marois et. al/NCR Canada)

Since the first planets outside the solar system were discovered in the 1990′s, scientists have hoped to find a planet that could support life. Because of the limited ability of the instruments used to search for extrasolar planets, almost all of the early planets discovered were very large and orbited very close to their host star. However, Kepler, which was constructed specifically to hunt for exoplanets, expanded the number of known extrasolar planets from just a few hundred to thousands.

To find extrasolar planets, Kepler examined some 150,000 stars in one small section of the galaxy using a technique called the transit method. Away from the distorting interference of Earth’s atmosphere, almost all stars shine at a consistent brightness. But a planet or other body passing in front of star will block some of the star’s light. Kepler looked for this dip in brightness. Unlike most of the first exoplanets discovered, the planets spotted by Kepler are of many sizes and distances from their home star.

Additional World Book articles:

• Kepler, Johannes
• Life (The search for life on other planets)
• In Search of Other Worlds (a Special Report)

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)

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

Dec. 14, 2011

The Kepler space telescope has found the first confirmed Earth-like planet orbiting in the “habitable zone” of a distant star. The planet, named Kepler 22b, is about 2 ½ times as large as Earth. 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’s sole mission, since the spacecraft’s launch in 2009, has been to spot planets circling distant stars.

Since the first extrasolar planet was discovered in the mid-1990′s, scientists have uncovered thousands of planets orbiting stars other than the sun. Because larger objects are easier to spot, most of the planets discovered so far are giants, many times larger than Jupiter, the largest planet in the solar system. Scientists have no way of knowing at this point if Kepler 22b has life. They think it is more likely that the planet is rocky, like Earth, rather than gaseous, like Neptune. It could even be an ocean world. They have calculated that if the planet has an atmosphere, the temperature there could be a pleasant 72 °F (22 °C).

The discovery comes just as the Allen Telescope Array (ATA) operated by the SETI Institute is back in operation. The 42 telescopes in the ATA, which were shut down early in 2011 because of budgetary problems, scan the sky for radio signals that could be signals from extraterrestrial beings. Over the next two years, SETI plans to focus the ATA at the top 1,000 habitable planets found by Kepler.

Additional World Book articles:

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