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)