Category Archives: Featured Articles

Finally Finding Other Earths [US News]

Looking for Earth-like planets isn’t anything new for astronomers. But it’s only been within the last few years that they’ve confidently identified candidates. The change from famine to feast is in large part due to NASA’s Kepler telescope, a mission that survived a number of challenges to become a reality. My US News article from earlier this year dives into how the hunt for exoplanets has changed and why Kepler has made such a significant contribution. The full article is below the image, which illustrates the sizes of a few identified exoplanets.

My exoplanet articles, as well as others, can be found by clicking the tags at the end of this post.

Credit: NASA/JPL-Caltech
Credit: NASA/JPL-Caltech

A Place Like Home


The hunt for planets like earth is rapidly locating other worlds.
When astronomer Alan Boss got an urgent call in September 1995 to review a provocative manuscript submitted to the scientific journal Nature, he had no idea that a revolution in the study of planets was about to start. The manuscript described observations by Swiss researchers at the Geneva Observatory who claimed to have found the first planet orbiting an ordinary star beyond the solar system. Boss, a planet formation expert at the Carnegie Institution for Science in Washington, D.C., was excited but skeptical. He was all too aware that several times since the 1960s, reports citing evidence of exoplanets, or planets orbiting a star other than the sun, had come to naught. By the fall of 1995, one research group was ready to throw in the towel after a 13-year search had failed to find even a single body.

That was deeply unsettling for astronomers like Boss. According to the leading theory of the solar system’s formation, which he had recently helped update, planets arise from a swirling disk of gas, dust, and ice that surrounds a young sun and should be common throughout the galaxy. So if exoplanets turned out to be truly scarce, researchers would have to face the fact that they had misunderstood how the solar system came to be. Not to mention that their odds of finding life outside the solar system would be drastically reduced. Science’s search for other civilizations would be in vain, and there would be no place for humans to go should living conditions on this crowded planet take a turn for the worse.

The intriguing manuscript sent to Boss summarized evidence that the tug of an unseen planet was causing a minuscule wobble in the motion of the star 51 Pegasi. Though he had a few questions for the authors, Boss could find no fatal flaw in their article. In early October, the Swiss team announced the discovery at a meeting in Florence; just 13 days later, a U.S. team led by astronomers Geoff Marcy, now at the University of California–Berkeley, and Paul Butler, now at Carnegie, said they had confirmed the wobble. News of the first bona fide planet discovered orbiting around a sunlike star thrilled astronomers and made the front page of newspapers around the world.

Abundant discoveries
Since that landmark finding, astronomers have discovered more than 750 exoplanets, with another 2,300 candidates awaiting confirmation. Researchers use an assortment of telescopes on the ground and in space in their search, but the recent flood of discoveries is largely credited to NASA’s Kepler telescope, which was launched early in 2009 and follows Earth in its path around the sun. Milestone discoveries have come furiously in the last couple of years: the first multiple-planet system around a sunlike star; the first rocky planet; the first exoplanet on which liquid water, a key ingredient for life, might exist.

“People call this the golden age of astronomy for exoplanets, but it’s beyond gold,” says Boss. Indeed, exoplanets now appear to be abundant beyond the wildest dreams of the most optimistic of planet hunters. A recent study estimates that on average, each of the more than 100 billion stars that glitter in the Milky Way harbors at least one planet. And the sheer diversity of the discoveries to date—how they’re distributed around a star, their density, and their spacing if they reside within a multiple-planet system—suggests that an entire solar system like Earth’s is not at all a rare entity, says planetary theorist Doug Lin of the University of California–Santa Cruz.

The orbs detected so far range from small rocky planets the size of Mercury to giant blobs of gas several times heavier than Jupiter. Many have great swooping orbits rather than a circular, sedate path like Earth’s that keeps temperature swings relatively mild, making life possible. This solar system is one of a “lucky subset with circular orbits,” says Marcy. Some members of the new celestial pantheon orbit two stars. Like Luke Skywalker’s home planet Tatooine in the Star Wars series, these planets are treated to a daily double feature: two sunsets and two sunrises. They and their stars emerged from the same primordial cloud of gas and dust, scientists believe; part of the material formed a planet while the rest coalesced into stars that remain gravitationally bound to each other though they now lie far apart.

Galvanized by the rapid progress, astronomers now are racing to find a potential twin to Earth. They’re pinning their hopes on the Kepler telescope, an observatory that almost didn’t get launched because few believed it would really work. Kepler is the brainchild of veteran planet hunter William Borucki, an astronomer at NASA’s Ames Research Center in Mountain View, Calif. Borucki’s tenacity kept the Kepler mission alive for 17 years after NASA repeatedly rejected the concept as too expensive and unlikely to find small planets.

Borucki first wrote about his vision for the telescope in 1984, a time when looking for planets seemed like the stuff of science fiction. He proposed that a properly positioned telescope, flying beyond Earth’s light-distorting atmosphere, could discover planets by staring continuously at one group of sunlike stars. Periodic dips in the brightness of individual stars would indicate a planet has passed in front of its sun or “transited,” blocking a tiny fraction of light. This reduction in brightness would reveal the planet’s size, while the frequency of the transits would indicate the planet’s orbital period and its distance from the star. The Hubble Space Telescope (story, Page 26) has sent back spectacular glimpses of galactic wonders for nearly two decades, but its small field of view and close orbit around Earth prevent it from continuously viewing any particular group of stars.

Borucki built a ground-based observatory and conducted experiments that proved the transiting method could work, though land-based telescopes could not be a long-term solution as the Earth’s atmosphere distorts the flickers of starlight. Finally, the project was approved, and in May 2009, the Kepler began regular operations. From its current vantage point, more than 30 million miles away, Earth is a tiny blue marble. Kepler’s primary mission is to focus on a narrow patch of roughly 156,000 stars in the Milky Way in hopes of finding other blue marbles that might mimic Earth in size, temperature, and orbit.

The telescope, which can record a reduction in starlight as small as 0.002 percent—akin to detecting an insect crawling across a car headlight from 3,000 miles away—had found 60 confirmed planets as of early 2012, as well as the more than 2,300 additional candidates. Initially, most were gaseous giants like Jupiter and Saturn. Then came smaller, rocky bodies whose molten surfaces cannot support life as humans know it. A precious few of these candidates of unknown size and composition reside in the so-called habitable zone, where water can exist as a liquid on a solid surface.

Lisa Kaltenegger, an astronomer at the Max Planck Institute for Astronomy in Germany and the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and an expert on the conditions necessary to detect life beyond Earth, remembers exactly where she was in 2009 when she heard about the spotting of the first potentially habitable exoplanet. About to hike across a glacier field and ice crevasse on South Island in New Zealand, she first checked her E-mail. A friend had written to say that astronomers had just determined that of one of the six planets circling a star called Gliese 581 was positioned within the habitable zone of the cool, red star. The first “Goldilocks” discovery—an exoplanet neither too hot nor too cold—opened “a new chapter in scientific discovery,” she says, that shifted focus from giant gaseous planets to rocky planets that could maintain water. “I allowed myself to completely unscientifically paint a picture in my head of what such a world could be like,” she recalls—a red sun and “loads of carbon dioxide obscuring the clear view.”

Of course, residing in the habitable zone doesn’t mean a planet actually harbors life, cautions Kaltenegger. That’s where monitoring planet transits across their stars offers a further advantage: The starlight filtering through, and reflecting off, a passing planet’s atmosphere can reveal the atmosphere’s composition, and indicate whether biological activity could have contributed to the chemical constituents. Astronomers have already recorded water vapor and sodium in the puffy atmospheres of gaseous Jupiter-like planets using transits. Now, they face the more difficult task of searching for tiny amounts of ozone and carbon dioxide, which can be produced by living organisms, in the much thinner atmosphere of rocky planets. Existing telescopes aren’t big enough; the effort must wait for the launch of the James Webb Space Telescope in 2018. Featuring a large, segmented mirror that will unfold in space, the Webb telescope will be able to make images (which Kepler doesn’t) and gather six times as much light as the Hubble while orbiting the sun some 940,000 miles from Earth.

Mass appeal. One reason early discoveries were dominated by big, gassy planets is that they exert the strongest tug on their parent stars, creating the most detectable wobble. The most common type of planet found by the Kepler is much smaller. To take the next step and determine whether a planet is gaseous or one of the rocky gems that could be an Earth analog, scientists must know both its mass and size. But the standard technique for determining mass—measuring how much the planet tugs on its star—doesn’t work for many of the Kepler planets because they are so puny.

A newer method relies instead on the extent to which planets in a solar system tug on each other. The heavier a planet, the more it delays or advances the transit times of the others in the system. That suggested a new way to figure out a planet’s mass. In April 2010, Jason Steffen, one of the researchers who devised the technique and is now an astrophysicist at the Fermi National Accelerator Laboratory in Batavia, Ill., found that the three planets in a system called Kepler-9 sometimes passed in front of their star ahead of or behind schedule. By analyzing the data further, Steffen was able to determine the mass of each planet.

The method worked especially well with the exoplanets in a solar system unveiled in February 2011 called Kep­ler-11, whose five innermost planets are packed so tightly that they all orbit their star at a distance shorter than that of the sun to its nearest planet, Mercury. Their mutual tug plays havoc with their transit times, enabling the team to determine their masses with unprecedented accuracy. In January 2012, Steffen’s team and two others announced that they’d identified 21 previously unknown planets and calculated the maximum mass of each orb.

Since many of the sunlike stars of interest are younger and rowdier than the one in this solar system—and thus more prone to sudden flares—scientists estimate that the Kepler telescope will have to watch twice as many transits as previously anticipated to be sure it’s really seeing planets rather than just stellar temper tantrums. But the Kepler mission is slated to end in November 2012. It would need to operate until mid-2016 to accurately estimate how many Earth-like planets are in the Milky Way, says Ron Gilliland, an adjunct professor of astronomy at Pennsylvania State University–University Park. With NASA strapped for cash (box, Page 10), it’s unclear whether that will happen. But space enthusiasts can take comfort from one fact that has been established, says planetary scientist Hal Levison of the Southwest Research Institute in Boulder, Colo. Even if a solar system with a habitable Earth twin turns out to be a 1 in 1 million find, he notes, with 100 billion-plus stars in the galaxy, that equals a lot of possibilities.

New Biomarkers to Identify Possible Life in Space [Scientific American]

Important progress has been made in our understanding and use of biomarkers, the signatures astronomers use to search for life in space. The work is all the more important given budget constraints that have cancelled space missions complementing the biomarker work by identifying life friendly star systems; improved biomarker searches may make up for fewer supporting missions.

Astronomers still hope to revive some version of Terrestrial Planet Finder [artist’s rendering below], but it would take a decade for the mission to get back on track, Marcy estimates. In the meantime studies by exoplanet researchers including Sara Seager of the Massachusetts Institute of Technology and Victoria Meadows of the University of Washington in Seattle are honing—and expanding—the list of compounds that may serve as biomarkers for exoplanets orbiting stars of different sizes and ages.

With the chances of looking for chemical markers of life beyond the solar system initially few and far between, “we want to make sure we have the best possible understanding of bio-signatures,” Meadows says. “We don’t want to be fooled.”

Much of the new work focuses on planets orbiting M dwarf stars, which are about one-half to one-tenth the sun’s mass and account for about 75 percent of all the stars in the galaxy. Because M dwarfs are much cooler than the sun, their habitable zones are only about one tenth as far from them as Earth lies from the sun.

The recent work on biomarkers, as well information about the cancellation of and existing plans for relevant space missions, are covered in my latest feature article for Scientific American.

Credit: NASA Science Missions

Private Space Telescope to Watch for Asteroids Heading Our Way [Nature]

A  nonprofit group has announced plans for the first privately funded mission to deep space. The telescope will identify and track 90 percent of the near-Earth asteroids 140 meters and larger, including those that could bash into our planet.

If you’ve got a hankering to protect Earth from wayward asteroids — and a few hundred million dollars to spare — the B612 Foundation would like to talk to you.

On Thursday the non-profit group announced plans to develop and launch the first privately funded deep-space mission, a space telescope that would find and observe 90% of all near-Earth asteroids larger than 140 metres across. The group — named after the mythical B612 asteroid that is home to the fictional character the Little Prince — comprises planetary scientists, engineers, former astronauts and former NASA officials.

The rest of the article can be found in my Nature recent article.

Source: Bell Aerospace
Source: Bell Aerospace

A New Test for Einstein with Free-floating Giant Black Holes [Science]

Are there massive black holes that move about the universe? In my recent article in Science notes, initial observations with the Hubble Space Telescope and follow-up data collection using NASA’s Chandra x-ray Observatory suggest this is the case. If so, then this would verify Einstein’s theory of general relativity under previously untested conditions.

Do Solo Black Holes Roam the Universe?

Even gravitational monsters can get the heave-ho. Two mysterious bright spots in a disheveled, distant galaxy suggest that astronomers have found the best evidence yet for a supermassive black hole being shoved out of its home.

Observations with NASA’s Chandra x-ray Observatory revealed that only one of the compact visible-light sources—a blob that lies about 8000 light-years from the galaxy’s estimated center—emits x-rays. The high-energy radiation is believed to be a sign that this blob is a supermassive black hole munching away on surrounding gas.

Even better than the image below, this short video explains how the big black hole may have formed.

Credit: NASA/CXC/SAO/F. Civano et al./STScI/CFHT
Credit: NASA/CXC/SAO/F. Civano et al./STScI/CFHT

Andromeda, Milky Way to Collide [Nature]

Our galaxy, the Milky Way galaxy, is set to change dramatically if new findings about the Andromeda galaxy’s direction and path are correct. My latest Nature article, excerpted below, reports the new findings and what they mean.

Andromeda on collision course with the Milky Way

It’s a definite hit. The Andromeda galaxy will collide with the Milky Way about 4 billion years from now, astronomers announced today. Although the Sun and other stars will remain intact, the titanic tumult is likely to shove the Solar System to the outskirts of the merged galaxies.

For decades, scientists have known that Andromeda is falling towards our home Galaxy at a rate of 110 kilometres per second and that the two might eventually collide as a result of their mutual gravity. But because astronomers could easily measure Andromeda’s velocity only along the line of sight to Earth, no one could be sure whether the future encounter would constitute a major merger, a near-miss or a glancing blow.

The image below is how the Milky Way may look after the Andromeda galaxy hurtles through.


Seeing Venus’ Silhouette [Science]

For the last time this century, Venus will pass across the face of the sun on June 5-6. Adorning the sun with a black beauty mark as big as a large sunspot, this 6.5-hour minieclipse (only part of which can be seen from the U.S. mainland) mimics the way most planets beyond the solar system are now detected. See my preview in Science magazine (pdf version available for those who do not subscribe).

Black Hole’s Newly Seen Y-Rays Suggest Recent Activity [Nature]

The quiescent monster at the center of the Milky Way—a supermassive black hole weighing about four million sun—used to be a lot more active.

Ghostly jets seen streaming from Milky Way’s core

Astronomers have found the best evidence yet that the dormant gravitational monster that lies at the centre of the Milky Way — a supermassive black hole known as Sagittarius A* — recently emitted a pair of γ-ray jets.

As they feed on stars and clouds of gas that stray too close, black holes at the centres of other galaxies create bright jets that can be seen across cosmic distances. But the Milky Way’s black hole shows no signs of such activity. Now, the Fermi Gamma-ray Space Telescope has picked up some faint γ-ray signals that suggest that Sagittarius A* has not always been so tranquil. The black hole could even have been active as recently as 20,000 years ago, after gulping down a gas cloud with a mass about 100 times that of the Sun, says Douglas Finkbeiner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Not part of my Nature article, but interesting nonetheless, is that the jets—composed of gamma-ray emitting charged particles—could have inflated the bubbles. To do so, the “faint, pathetic jets” observed by Fermi would have had to be much brighter, and carried more energy, in the past, says Finkbeiner. “We infer that that most of the time over the last million years, the jets have been perhaps ten times as bright.”

He adds that Fermi does not see the jets within about 10,000 light-years of the galaxy’s center, an indication that Sagittarius A* switched off its activity some 20,000 to 30,000 years ago, assuming the jets travel at about one–third the speed of light.

The artist’s illustration below, which shows the jets going all the way to the Milky Way’s center, reflects how the jets used to appear, not how they appear now.

Credit: David A. Aguilar (CfA)
Credit: David A. Aguilar (CfA)

NASA’s Visit to Solar System’s 2nd Biggest Asteroid Vesta Yields New Data about Asteroid Families [Nature]

Vesta confirmed as venerable planet progenitor

NASA’s Dawn spacecraft won’t end its 13-month-long visit to Vesta, the Solar System’s second biggest asteroid, until August, but researchers have now solidified the rock’s reputation as an archetype for understanding planetary evolution. In six reports in the 11 May edition of  Science, Dawn mission scientists have confirmed several long-held assumptions about Vesta and detailed some puzzles about the roughly 520-kilometer-diameter body.

My article highlights Vesta’s importance in our understanding of asteroids and meteorites, as well some remaining mysteries that continued study may illuminate.

Update: The Knight Science Journalism Tracker once again notes my science reporting by highlighting this and my previous Vesta-related story:

NatureNews (blog) Ron Cowen: Vesta confirmed as venerable planet progenitor ; the ‘confirmed’ in the hed is a good way to say this is not surprise news, but incremental news. Cowen, on constant prowl for news before it is wide news, includes a link to a previous post on Vesta’s topography and what it might mean, from meetings last fall.


Where’s the Dark Matter? New Study Finds None Near the Solar System [Nature]

Survey finds no hint of dark matter near Solar System

In the largest survey of its kind to date, astronomers scouring the space around the Solar System for signs of dark matter — the hypothetical material believed to account for more than 80% of the mass in the Universe — have come up empty-handed.

If confirmed, the surprising result would upend a long-established consensus, researchers not involved in the study say.  For decades, cosmic theories have relied on dark matter — which exerts gravitational pull but emits no light — to be the hidden scaffolding that explains how structure arose in the Universe, how galaxies formed and how the rapidly spinning Milky Way manages to keep from flying apart. Without dark matter, theorists say, the visible material in the Universe, such as stars and gas, would not have the heft to do the job alone.

The rest of the article explains how the research was conducted and what the scientific community thinks of the finding.

Credit: ESO/H.H.Heyer
Credit: ESO/H.H.Heyer