8. Habitable Planets

Search For Habitable Planets

In the Exoplanet Transits investigation, here is data to generate a light curves for various exoplanets:

  • images provided by the Zen Observatory, from their TrES-3 page.
  • images of GJ 436b from Bareket Observatory (Israel) on 2010 Feb 20 (85 Mb zipped). Included in the zip file is a finding chart and an image indicating where aq suitable reference star is, as well as the "check" star GJ 436).
  • The MicroObservatory project has a number of exoplanet observations. Click on their "Get Images" link, then click on "Image Archive" and look for "Other Worlds."

2021-07-26. - Articles in Eos/AGU:  Unveiling the Next Exoplanet Act, by Heather Goss. Excerpt: ...our August issue is all about exoplanets—what we know and what awaits us over the launch horizon. Who gets the first peek through James Webb Space Telescope (JWST)? In March, the proposals selected for the first observing cycle were announced. Meet the slate of scientists who will be pointing the telescope at other worlds, and read what they hope to learn in “Overture to Exoplanets." ...In “The Forecast for Exoplanets Is Cloudy but Bright,” we learn the immense challenge posed by exoplanet atmospheres, when researchers are still struggling to understand the complex dynamics of clouds on our own planet. ...And in “Exoplanets in the Shadows,” we look at the rogues, the extremes, and a new field being coined as necroplanetology. See also Oddballs of the Exoplanet Realm

2021-06-21. [https://eos.org/articles/gap-in-exoplanet-size-shifts-with-age] - Gap in Exoplanet Size Shifts with Age. Source: By Katherine Kornei, Eos/AGU. Excerpt: Smaller planets are scarcer in younger systems and larger planets are lacking in older systems, according to new research that analyzed hundreds of exoplanets. ...Planets just a bit larger than Earth appear to be relatively rare in the exoplanet canon. A team has now used observations of hundreds of exoplanets to show that this planetary gap isn’t static but instead evolves with planet age—younger planetary systems are more likely to be missing slightly smaller planets, and older systems are more apt to be without slightly larger planets. This evolution is consistent with the hypothesis that atmospheric loss—literally, a planet’s atmosphere blowing away over time—is responsible for this so-called “radius valley,” the researchers suggested....

2021-05-21. [https://eos.org/articles/record-setting-flare-spotted-on-the-nearest-star-to-the-sun] - Record-Setting Flare Spotted on the Nearest Star to the Sun. Source: By Katherine Kornei, Eos/AGU. Excerpt: As stellar neighbors go, the Sun is a pretty good one—it occasionally produces a sizeable solar flare, but mostly, it leaves Earth well enough alone. The Proxima Centauri solar system isn’t so lucky, however: Blasts of electromagnetic radiation from Proxima Centauri, the next nearest star to our own, can be potentially lethal to nearby planets. Researchers recently spotted the brightest stellar flare ever detected from Proxima Centauri. That flare might have contributed to stripping away the atmosphere of one of its planets, a roughly Earth mass world that potentially hosts liquid water on its surface. ...Destroyer of Atmospheres ...Proxima Centauri’s faintness stems from its low mass—it’s what astronomers refer to as an M dwarf star, defined as having a mass between roughly 10% and 50% the mass of the Sun. M dwarf stars are the most common stars in the Milky Way, but they come with a reputation, said Meredith MacGregor, an astronomer at the University of Colorado Boulder. “M dwarfs are vastly more active than the Sun.” That means they regularly emit stellar flares, blasts of electromagnetic radiation launched by their host star’s magnetic field. These streams of photons can be destructive, said MacGregor. When high-energy ultraviolet radiation collides with a planet’s atmosphere, it can disassociate molecules like water and ozone, splitting them into their constituent atoms. Some of those lighter atoms can then drift away and escape. “You can basically erode away the atmosphere of a planet,” said MacGregor.... 

2020-11-05. Earth-size Planets are Common, Kepler Retrospective Finds. Sky and Telescope Magazine. Excerpt: ...NASA’s Kepler telescope was retired a few years ago, but ongoing analyses of its data, both by professional astronomers and citizen scientists, are still producing new results. ...Kepler has found more than 2,600 exoplanets (and counting). Now, an international collaboration led by Steve Bryson, a researcher at NASA Ames, has announced a refined estimate. The team, including NASA scientists, SETI researchers, academics, former-Keplerites, and other planet hunters, performed a statistical analysis that combined Kepler’s planet catalog and stellar data from the European Space Agency’s Gaia observatory. They found that about half of the Sun-like stars in our galaxy could have a rocky planet in their habitable zones. ...The study, soon to be published in The Astronomical Journal, predicts that there are at least 300 million habitable-zone rocky worlds in the Milky Way. A handful of these are within a few light-years of Earth. This result assumes that the section of the sky Kepler monitored for four years is representative of the whole galaxy.... [https://skyandtelescope.org/astronomy-news/kepler-retrospective-earth-like-planets-common/] See also The New York Times article https://www.nytimes.com/2020/11/05/science/astronomy-exoplanets-kepler.html

2020-04-20. The Case of the Disappearing Exoplanet. By Robin George Andrews, New York Times. Excerpt: Humanity’s growing tally of exoplanets — worlds seen orbiting other stars — stands at 4,151. Most were found indirectly, as they passed in front of their stars and cast a telltale shadow, or as they caused their star to wobble as they swung around it. Only 50 have been directly imaged through a telescope. Directly imaging an exoplanet was first achieved in two discoveries announced simultaneously in 2008. ...a solitary planet dancing around the star Fomalhaut was spotted by the Hubble Space Telescope. Fomalhaut b, as the latter was named, appeared to be a colossal world, potentially as massive as three Jupiters, zipping along the inner edge of a giant doughnut of debris. ... András Gáspár, an astronomer at the University of Arizona, was looking at Hubble’s images of the Fomalhaut system taken up through 2014, on the off chance that someone missed something. To his surprise, Fomalhaut b was nowhere to be found in 2014.... [https://www.nytimes.com/2020/04/20/science/fomalhaut-exoplanet-asteroid.html

2020-02-26. This rainy exoplanet could be ripe for life. By Daniel Clery. Science Magazine. Excerpt: A nearby exoplanet with rainclouds in its atmosphere may have habitable conditions at its surface, researchers report today. The planet, dubbed K2-18b, is 124 light-years away and 2.6 times the radius of Earth. Last year, astronomers detected clouds of liquid water in the planet’s hydrogen-rich atmosphere, a first for such a small planet. [https://www.sciencemag.org/news/2019/09/hints-rain-clouds-found-small-alien-world] ...Now, a team of researchers in the United Kingdom describe in The Astrophysical Journal Letters how they calculated a range of possible atmospheres for the planet, based on its mass, size, and previously measured spectra of light that passed from K2-18b’s star through its atmosphere. (Molecules in the planet’s atmosphere absorb certain frequencies of light, so if the starlight passes through it on its way to Earth, the light’s spectrum can reveal those molecules.) They then used those possibilities to limit what conditions could exist in the planet’s interior. Their conclusion: The heart of K2-18b could be anything from a ball of almost pure iron with a hefty hydrogen atmosphere, to something more Neptune-like, to a water world with a lighter atmosphere and ocean conditions similar to Earth.... [https://www.sciencemag.org/news/2020/02/rainy-exoplanet-could-be-ripe-life] 

2020-01-10. A teenager discovered a new planet on the third day of his NASA internship. By Lateshia Beachum, The Washington Post.

2019-09-11. Water found for first time on potentially habitable planet. By Pallab Ghosh, BBC News. 

2019-07-29. NASA’s TESS Satellite Spots ‘Missing Link’ Exoplanets. By Dennis Overbye, New York Times. 

2019-04-04. Astronomers spy an iron planet stripped of its crust around a burned-out star. By Daniel Clery, Science Magazine. 

2019-03-05. The first planet Kepler spotted has finally been confirmed 10 years later. By Lisa Grossman, Science News. 

2019-01-14. Modeling the Climates of Worlds Beyond Earth. By Katherine Kornei, Eos/AGU. 

2019-01-07. Another Day, Another Exoplanet: NASA’s TESS Keeps Counting More. By Dennis Overbye, The New York Times. 

2018-11-14. Super-Earth spied in the second-closest star system from the sun. By Daniel Clery, Science Magazine. 

2018-10-30. NASA Retires Kepler Space Telescope, Passes Planet-Hunting Torch. NASA RELEASE 18-092. 

2018-10-03. First moon outside the solar system could be as big as Neptune. By Joshua Sokol, Science Magazine. 

2018-09-24. How Well Can the Webb Telescope Detect Signs of Exoplanet Life? By Lucas Joel, Eos/AGU. 

2018-09-20. NASA’s TESS Starts Collecting Planets. By Dennis Overbye, The New York Times. 

2018-08-01. The Kepler Revolution. By Kimberly M. S. Cartier, Eos/AGU.

2018-03-28. NASA’s new satellite brings the search for Earthlike exoplanets closer to home. By Daniel CleryMar, Science. 

2018-03-26. Meet TESS, Seeker of Alien Worlds. By Dennis Overbye, The New York Times. 

2018-01-24. Looking to the Future of Exoplanet Science. By Kimberly M. S. Cartier, Eos/AGU. 

2017-12-14. Artificial Intelligence, NASA Data Used to Discover Eighth Planet Circling Distant Star. By NASA RELEASE 17-098. 

2017-11-15. Nearby Earth-sized world may be the best candidate yet in the search for alien life. By Loren Grush, The Verge. 

2017-06-22. Ten Earth-Sized Planets Found by Exoplanet-Hunting Telescope. By JoAnna Wendel, Earth & Space Science News, EoS, AGU. 

2017-06-19. Earth-Size Planets Among Final Tally of NASA’s Kepler Telescope. By Dennis Overbye, The New York Times.

2017-05-10. The Harmony That Keeps Trappist-1’s 7 Earth-size Worlds From Colliding. By Kenneth Chang, The New York Times. 

2017 March. Whole New Worlds: An Aladdin History of ExoplanetsVideo by A Capella Science, Trudbol, SamRobson, Gia Mora, (https://www.youtube.com/watch?v=gai8dMA19Sw).  8.5 min long.

2017-02-22. NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star. NASA RELEASE 17-015. 

2016-08-07. Martians Might Be Real. That makes Mars exploration way more complicated. By Kevin Carey, WIRED.

2016-07-20. NASA’s Hubble Telescope Makes First Atmospheric Study of Earth-Sized Exoplanets. NASA RELEASE 16-076.

2016-05-16. Aging Stars Make New Habitable Zones. By JoAnna Wendel, EoS-Earth & Space Science News (AGU). 

2016-02-18. Berkeley Lab, UC Berkeley Scientists to Participate in New NASA Space Telescope Project. By Glen Roberts Jr., Berkeley Lab News Center.

2015-01-06. So Many Earth-Like Planets, So Few Telescopes. By Dennis Overbye, The New York Times. Front page story.

2014-07-10. NASA Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars. Excerpt: Repeated high-resolution observations made by NASA’s Mars Reconnaissance Orbiter (MRO; http://www.nasa.gov/mro ) indicate the gullies on Mars’ surface are primarily formed by the seasonal freezing of carbon dioxide, not liquid water. The first reports of formative gullies on Mars in 2000 generated excitement and headlines because they suggested the presence of liquid water on the Red Planet, .... Mars has water vapor and plenty of frozen water, but the presence of liquid water on the neighboring planet, a necessity for all known life, has not been confirmed. This latest report about gullies has been posted online by the journal Icarus. "As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water," said lead author Colin Dundas of the U.S. Geological Survey's Astrogeology Science Center in Flagstaff, Arizona. "...we saw that the activity occurs in winter." Dundas and collaborators used the High Resolution Imaging Science Experiment (HiRISE; http://hirise.lpl.arizona.edu ) camera on MRO to examine gullies at 356 sites on Mars, beginning in 2006. ...Using dated before-and-after images, researchers determined the timing of this activity coincided with seasonal carbon dioxide frost and temperatures that would not have allowed for liquid water. ...The findings in this latest report suggest all of the fresh-appearing gullies seen on Mars can be attributed to processes currently underway, whereas earlier hypotheses suggested they formed thousands to millions of years ago when climate conditions were possibly conducive to liquid water on Mars.... http://www.nasa.gov/press/2014/july/nasa-spacecraft-observes-further-evidence-of-dry-ice-gullies-on-mars/#.U_t1t0iprZF. NASA RELEASE 14-191.

2014-04-17. First Earth-Size Planet in 'Habitable Zone'. Excerpt: Using NASA's Kepler Space Telescope, astronomers have discovered the first Earth-size planet orbiting a star in the "habitable zone" -- the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The discovery of Kepler-186f confirms that planets the size of Earth exist in the habitable zone of stars other than our sun. While planets have previously been found in the habitable zone, they are all at least 40 percent larger in size than Earth and understanding their makeup is challenging. Kepler-186f is more reminiscent of Earth. "The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth," said Paul Hertz, NASA's Astrophysics Division director at the agency's headquarters in Washington. "Future NASA missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind's quest to find truly Earth-like worlds." http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=330. By NASA Kepler mission. See NASA RELEASE 14-111. See also: http://kepler.nasa.gov/news/keplerinthenews/index.cfm?FuseAction=ShowNews&NewsID=332.

2013-04-18. Kepler's Smallest Habitable Zone Planets.    NASA    Kepler mission    ...We're a step closer to knowing if our galaxy is home to a multitude of planets like Earth or if we are a rarity. The three habitable zone super-Earth-size planets are in two systems containing a total of seven newly discovered planets...Star Kepler-62 is not Sun-like: just 2/3 the size of the Sun, cooler, older, and only 1/5 as bright. Planet Kepler-62f, 40% larger than Earth, the smallest known habitable zone exoplanet, orbits every 267 days. Planet Kepler-62e, about 60% larger than Earth, orbits every 122 days in the the habitable zone's inner edge. http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=243

2009 October 19. Many More Planets Found Outside Solar System. NY Times. Excerpt: WASHINGTON(AP) -- European astronomers have found 32 new planets outside our solar system, adding evidence to the theory that the universe has many places where life could develop. Scientists using the European Southern Observatory telescope didn't find any planets quite the size of Earth or any that seemed habitable or even unusual. But their announcement increased the number of planets discovered outside the solar system to more than 400.
Six of the newly found planets are several times bigger than Earth, increasing the population of so-called super-Earths by more than 30 percent. Most planets discovered so far are far bigger, Jupiter-sized or even larger.
Two of the newly discovered planets were as small as five times the size of Earth and one was up to five times larger than Jupiter.
...What astronomers said is especially exciting is that about 40 percent of sun-like stars have planets that are closer to being Earth-sized than the size of Jupiter. Jupiter's mass is more than 300 times that of Earth's....

2009 Aug 31. A Doomed Planet, and Scientists Are Lucky to Have Spotted It. By Kenneth Chang. Excerpt: Were astronomers just lucky when they discovered the planet WASP-18b? ...about 10 times the mass of Jupiter), close to the parent star (about 1.9 million miles away, or just one-fiftieth of the distance between the Sun and Earth) and hot (3,800 degrees Fahrenheit). About one-quarter of the nearly 400 planets discovered so far have been such "hot Jupiters. But as an international team of astronomers looked more closely, they became more surprised that they had seen WASP-18b at all. The tidal forces between a star and a planet dissipate energy, and WASP-18b is so close that it should fall into its host star in less than a million years - an eye blink on the cosmic scale....

2009 July 20. Searching for Extraterrestrial Life. By Claudia Dreifus, The NY Times. Excerpt: At his day job, Alan Boss of the Carnegie Institution of Washington studies how stars and planets are born. In recent years, he has consulted with scientists for NASA’s Kepler space telescope on their mission of finding planets outside our solar system that might be hospitable to life. Mr. Boss, a 58-year-old astronomer and theoretical astrophysicist, was in New York City recently to promote his new book, “The Crowded Universe: the Search for Living Planets,” about the scientific hunt for extraterrestrial life....
A. Now we’re ready to do some science! The big payoff is coming!
Kepler’s mission is to detect planets outside our solar system that roughly have the same size, conditions and distance from their stars as Earth. We think the probability of finding extraterrestrial life would be best on Earth-like planets. From previous observations, we know of about 330 “extra-solar” planets. Kepler is likely to send us evidence of hundreds of Earth-like planets revolving around hundreds of Sun-like stars.
A. From ground-based observations, we know that Earth-like planets are going to be quite common. Estimates are that “earths” probably occur in 10 to 20 percent of the stars. My feeling is that if you have that many earths and you have some prebiotic soup, comets that bring in the organic chemicals that you need to have life, something is going to grow....

2009 June 17. Exoplanet Has Oddball Orbit. By Nancy Atkinson, Universe Today. Excerpt: In what might be a evidence of planetary billiards, astronomers have found an exoplanet with an extremely odd orbit. The question is, was this planet the cue ball or the object ball? While most planets orbit around a star's mid-section, this one – called XO-3b — is tilted about 37 degrees from the star's equator. It's also a massive planet, about 10 times the size of Jupiter. Such a misalignment must have occurred as a result of a disturbance, such as a collision with another object, sometime after the planet's formation. But astronomers say they don't yet know what caused the unusual orbit of XO-3b.
...The planet was discovered back in 2007 using the transit method by measuring how the star is dimmed by the planet passing in through the line-of-sight between Earth and the star.
...But to go one step further and measure the angle of its orbit, meant that "we have to be sneaky about it," said MIT physicist Joshua Winn, who led the team that measured the planet's tilted orbit. It turns out that if a planet crosses the star's disk at an angle to the star's own rotation, it causes a distinctive pattern of change in the overall color of the star, as measured by a highly sensitive spectrograph, because of the Doppler shifts caused by the star's rotation.
...Such "hot Jupiters" ...could not have formed in the places they are seen now, according to accepted planet-formation theory. They must have formed much further out from the star, then migrated inward to their present positions. Astronomers have come up with different mechanisms to account for the migration: the gravitational attraction of other planets as they passed close by, or the attraction of the disk of dust and gas from which the star and its planets formed.
Close encounters with other planets could greatly amplify a slight initial tilt, but attraction from the disk of material could not. Likely, a cataclysmic event occurred in this planet's past....

2009 April 21. Astronomers Find Planet Closer to Size of Earth. By Dennis Overbye, The NY Times. Excerpt: European astronomers said Tuesday that they had discovered the smallest planet yet found orbiting another star. The planet could be as little as only 1.9 times as massive as the Earth and belongs to a dim red star known as Gliese 581, which lies about 20 light-years from Earth in the constellation Libra.
The star was already know to harbor at least three more massive planets. The new planet, known as Gliese 581e, is probably rocky like the Earth, but it lies in such a close orbit — only three million miles from its star — that it is surely blasted with too much radiation and heat to be livable.
...Astronomers said the discovery was more encouragement that the galaxy was full of small-mass planets and that with more time and improved instruments like the Kepler satellite, recently launched by NASA, they would eventually find Earth-like planets in orbits suitable for life around other stars.
“Finding Earth-like planets with lukewarm temperatures is the next great goal,” Geoff Marcy, of the University of California, Berkeley, a planet-hunting rival of Dr. Mayor’s, said in an e-mail message....

2009 March 2. In a Lonely Cosmos, a Hunt for Worlds Like Ours. By Dennis Overbye, The NY Times. Excerpt: ...Presently perched on a Delta 2 rocket at Cape Canaveral is a one-ton spacecraft called Kepler. If all goes well, the rocket will lift off about 10:50 Friday evening on a journey that will eventually propel Kepler into orbit around the Sun. There the spacecraft’s mission will be to discover Earth-like planets in Earth-like places — that is to say, in the not-too-cold, not-too-hot, Goldilocks zones around stars where liquid water can exist.
The job, in short, is to find places where life as we know it is possible.
“It’s not E.T., but it’s E.T.’s home,” said William Borucki, an astronomer at NASA’s Ames Research Center at Moffett Field in California, who is the lead scientist on the project. Kepler...will look for tiny variations in starlight caused by planets passing in front of their stars. Dr. Borucki and his colleagues say that Kepler could find dozens of such planets — if they exist. The point is not to find any particular planet — hold off on the covered-wagon spaceships — but to find out just how rare planets like Earth are in the cosmos.
...Kepler’s strategy is, in effect, to search for the shadows of planets. The core of the spacecraft, which carries a 55-inch-diameter telescope, is a 95-million-pixel digital camera. For three and a half years, the telescope will stare at the same patch of sky about 10 degrees, or 20 full moons, wide, in the constellations Cygnus and Lyra. It will read out the brightnesses of 100,000 stars every half-hour, looking for the telltale blips when a planet crosses in front of its star, a phenomenon known as a transit.
To detect something as small as the Earth, the measurements need to be done with a precision available only in space, away from the atmospheric turbulence that makes stars twinkle, and far from Earth so that our home world does not intrude on the view of shadow worlds in that patch of sky. It will take three or more years — until the end of Barack Obama’s current term in office — before astronomers know whether Kepler has found any distant Earths....

2008 November / December. The stars her destination. BY ROBERTA KWOK, California Alumni Magazine. A business major's epiphany leads her to become a NASA scientist. Excerpt: Natalie Batalha's worst enemy is the clock. Installed around the corner from her office at NASA Ames Research Center, a looming LED display is counting the days, hours, minutes and seconds until the launch of the Kepler Mission: NASA's first attempt to find habitable Earth-like planets in our galaxy.
"It's terrible," says Batalha '89, who has been working on the mission for eight years. "It recently rolled over from 300 to 299, and I could just feel my blood pressure rising."
When the clock runs down to zero next spring, Batalha will stand with her family at Cape Canaveral in Florida to watch Kepler's take-off. The spacecraft's telescope will peer at one slice of the sky for three-and-a-half years, to look for signs of terrestrial planets using a technique called the transit method. Batalha likens the process to a fly passing in front of a car's headlight: Every time a planet passes in front of the star it orbits, it dims the star's light a little, the same way a fly would dim a headlight as it flew past. As part of preparation for launch, Batalha has been choosing-very, very carefully-the 170,000 stars that Kepler will observe from among the 13 million in its field of view.
Batalha may be feeling the pressure, but it doesn't show. Her voice has the warm, calming quality of a public radio host, and when she demonstrates the orbit of a planet around a star, her movements are poised and exact. "Can you imagine that within your lifetime, you will probably be able to look up in the sky and say, 'That star right there has a habitable Earth-like planet orbiting it'?" asks Batalha, an associate professor at San Jose State University. "That's astounding. It's going to change the way people understand their place in the universe."....

Articles about planet finding and articles specifically about the Kepler mission may be found on the NASA Kepler mission website.   


  Articles from 2008–present

NASA's Kepler mission to find Earth size planets in the habitable zones of stars.

Transit of HD209458
- supplement for investigation Exoplanet Transits.
Part I - Plot a Transit Light Curve, step C, John Kolena, HOU TRA, has found that better reference stars are at:
x = 185, y = 181 or x = 311, y = 276
rather than the one at x = 564, y = 266 (as originally suggested)