A ‘Super-Earth’ with an Atmosphere

Picking up on yesterday’s theme of planetary detections from ground-based observatories, we now get word of the detection of a transiting ‘super-Earth’ — one that may well have an atmosphere we can study — with the kind of equipment many amateurs already use to observe the sky. The new world is GJ 1214b, about 6.5 times as massive as the Earth, orbiting a small M-dwarf about a fifth the size of the Sun some forty light years from Earth.

But there’s more, a good deal more. At a distance of 1.3 million miles, the planet orbits its star every 38 hours, with an estimated temperature a little over 200 degrees Celsius. Because GJ 1214b transits the star, astronomers are able to measure its radius, which turns out to be 2.7 times that of Earth. The density derived from this suggests a composition of about three-fourths water and other ices and one-fourth rock. Some of the planet’s water should be in the form of exotic materials like Ice VII, a crystalline form of water that is found at pressures greater than 20,000 Earth atmospheres:

“Despite its hot temperature, this appears to be a waterworld,” said Zachory Berta, a graduate student at the Harvard-Smithsonian Center for Astrophysics (CfA) who first spotted the hint of the planet among the data. “It is much smaller, cooler, and more Earthlike than any other known exoplanet.”

That’s quite a find for the MEarth Project, which uses an array of eight 16-inch telescopes that monitor a list of 2000 red dwarf stars. The MEarth array is located at the top of Mount Hopkins, Arizona. MEarth looks for the tiny drop in brightness that indicates a transit, using data processing technologies to extract the planetary signature. If ever there was a find that should galvanize the amateur astronomy community, it’s this one, as David Charbonneau (CfA), who heads MEearth, is quick to note:

“Since we found the super-earth using a small ground-based telescope, this means that anyone else with a similar telescope and a good CCD camera can detect it too. Students around the world can now study this super-earth!”

gj1214

Image: This artist’s impression shows how the newly discovered super-Earth surrounding the nearby star GJ1214 may look. Discovered by the MEarth project and investigated further by the HARPS spectrograph on ESO’s 3.6-metre telescope at La Silla, GJ1214b is the second super-Earth exoplanet for which astronomers have determined the mass and radius, giving vital clues about its structure. It is also the first super-Earth around which an atmosphere has been found. Credit: ESO/L. Calçada.

But detecting the transit was only the first step in the process of collaboration between small telescopes and larger instrumentation. Confirming the MEarth find involved studying it with the HARPS spectrograph attached to the European Southern Observatory’s 3.6-meter telescope at La Silla. HARPS data were also crucial in determining the mass and radius of CoRoT-7b.

Sifting through this material, what stands out is that the radius measured for GJ 1214b is larger than expected by current models. Remember, this is the second time we’ve found a transiting super-Earth, the first being CoRoT-7b. The latter has a similar mass but the radius of GJ 1214b is much larger. Indications are that a surrounding atmosphere some 200 kilometers thick is adding to the drop in stellar light measured in these transits. Charbonneau again:

“This atmosphere is much thicker than that of the Earth, so the high pressure and absence of light would rule out life as we know it, but these conditions are still very interesting, as they could allow for some complex chemistry to take place.”

We should be able to learn more about this atmosphere, for GJ 1214b is close enough to Earth that the Hubble telescope should be able to characterize its atmosphere. The paper is Charbonneau et al., “A Super-Earth Transiting a Nearby Low-Mass Star,” Nature 462 (17 December 2009), pp. 891-894 (abstract).

tzf_img_post

Planets Around Sun-like Stars

What jumps out at the reader when examining yesterday’s exoplanet news is not so much that we’ve found as many as six low-mass planets, but that the two stars involved are both near twins of the Sun. Steven Vogt (UC-Santa Cruz) and Paul Butler (Carnegie Institution of Washington) led this work, and Vogt is quick to point out that two of the planets are ‘super-Earths,’ the first we’ve ever found around stars so similar to our own. Vogt notes this has implications for the broader hunt for planets that could sustain life:

“These detections indicate that low-mass planets are quite common around nearby stars. The discovery of potentially habitable nearby worlds may be just a few years away.”

A Bonanza Around 61 Virginis

And Sun-like they are, these stars. 61 Virginis, 28 light years from Earth, has long fascinated astrobiologists because it is more similar to the Sun than any of our nearest neighbors in terms of age, mass and other properties. Moreover, a separate team working with the Spitzer Space Telescope has discovered a thick ring of dust around 61 Vir at about 80 AU, twice the distance of Pluto from the Sun. No doubt we’re looking at the result of cometary collisions in the outer reaches of this interesting system.

61 Vir is now known, from this ground-based radial velocity work using data from the Keck Observatory as well as the Anglo-Australian Telescope, to host at least three planets, ranging in mass from five to 25 times that of Earth. And UC-Santa Cruz postdoc Eugenio Rivera notes that “Spitzer’s detection of cold dust orbiting 61 Vir indicates that there’s a real kinship between the Sun and 61 Vir.” Indeed, Rivera’s simulations on this system show that a habitable Earth-like world could readily exist in the region between the newly discovered planets and the outer dust disk.

61Virbcd_orbits

Image: A comparison of the orbits of the planets of 61 Vir with the inner planets in our Solar System. All three planets discovered to date in this system would lie inside the orbit of Venus. Credit: University of New South Wales/Carnegie Institution.

The Case of HD 1461

The second star in question is HD 1461, like 61 Vir a near twin of the Sun, some 76 light years away. We’ve found one definite planet there, a world of 7.5 Earth masses, although we lack the data to know whether this is a ‘super-Earth’ or something closer to Uranus or Neptune. Indications of two other planets are also present. Whatever the case, note the precision involved in this work. The inner 61 Vir planet, says Butler, produced a planetary signal that is among the two or three lowest-amplitude signals that have ever been identified. Butler goes on to make this remarkable observation:

We’ve found there is a tremendous advantage to be gained from combining data from the AAT and Keck telescopes, two world-class observatories, and it’s clear that we’ll have an excellent shot at identifying potentially habitable planets around the very nearest stars within just a few years.”

This is good news indeed, especially coupled with the growing belief that as many as half of nearby stars have detectable planets with masses less than or equal to Neptune’s. Ponder the fact that this is all being done with ground-based telescopes using the radial-velocity method. In this case, the team then matched their work with measurements from robotic telescopes in Arizona to ensure there was no brightness variability in either of the stars in question. The fact that there was not rules out patterns of dark spots on these stars that could have thrown the planetary findings into question.

Tuning Up Ground-Based Detections

You’ll want to read Greg Laughlin’s brief comment on the finds on his systemic site (Laughlin was a member of the UC-Santa Cruz team and a co-author of the two papers the work has produced). He notes that our ground-based observing techniques have now been refined to the point where Earth-mass objects around nearby stars are within reach:

“It’s come down to a neck-and-neck race as to whether the first potentially habitable planets will be detected from the ground or from space,” Laughlin said. “A few years ago, I’d have put my money on space-based detection methods, but now it really appears to be a toss-up. What is truly exciting about the current ground-based radial velocity detection method is that it is capable of locating the very closest potentially habitable planets.”

For newcomers here, I’ll also note that the Lick-Carnegie Exoplanet Survey Team has created an excellent tool available to the public that allows anyone so inclined to search for extrasolar planet signals by exploring real data sets. The Systemic Console is available through the systemic site.

The papers, both slated for publication in the Astrophysical Journal, are Vogt et al., “A Super-Earth and two Neptunes Orbiting the Nearby Sun-like star 61 Virginis,” (preprint), and Rivera et al., “A Super-Earth Orbiting the Nearby Sun-like Star HD 1461,” (preprint).

A Jupiter in a Circular Orbit

But the good news doesn’t stop here. A Jupiter-mass planet has been discovered around the G5V star 23 Librae in a fourteen-year orbit similar to Jupiter’s ten-year period. This one is especially intriguing because it shows we’re beginning to be able to detect the signatures of solar systems that are much like our own. Hugh Jones (University of Hertfordshire) comments:

“Since Jupiter dominates the signal from our Solar System, we are now in a position to quantify how common planets like Jupiter are around stars like our Sun. Compared to the Solar System, most extrasolar systems look odd, with planets in very small or very elliptical orbits. In contrast, this new planet has an orbit that is both large, and nearly circular — for the first time we are beginning to see systems that resemble our own.”

This work is also a collaboration between the Anglo-Australian Telescope and the Keck Telescope, and the system they’re reporting on is an unusual one in other ways. A previously known giant planet has been discovered orbiting 23 Lib in an eccentric eight-month orbit. “This makes this yet another unexpected oddball – a system with a circular Jupiter-like planet, but with an interior planet in an eccentric orbit,” notes Rob Wittenmyer of the University of New South Wales.

The paper on the 23 Lib discovery is Jones et al., “A long-period planet orbiting a nearby Sun-like star,” submitted to Monthly Notices of the Royal Astronomical Society (preprint).

tzf_img_post

Propulsion from the Quantum Vacuum?

With WISE now on its way (a spectacular launch in the dark at Vandeberg Air Force Base), we now turn to the realm of exotica. Specifically, can we find ways to exploit the quantum vacuum to produce propulsion? I’ve seldom had such a flurry of interested emails than what followed the appearance of a paper by Alex Feigel, recently put up on the arXiv server. Feigel (Soreq Nuclear Research Center, Israel) discusses modifying the momentum of the quantum vacuum, an idea dear to that segment of the interstellar propulsion community that focuses on ‘propellantless’ propulsion.

Some background: Heisenberg’s uncertainty principle implies that it is impossible to achieve an absolute zero electromagnetic energy state in the vacuum of space. The measurement of the Casimir effect in 1997 demonstrated that a force would be exerted between two narrowly separated conducting plates. Indeed, at the micron scale, such plates are squeezed together as longer wavelength waves are excluded. The possibility of creating net propulsive forces using this energy was studied by NASA’s Breakthrough Propulsion Physics program during its all too brief lifetime at the agency.

A vacuum, then, is not free of energy, but seethes with electromagnetic waves coming into existence and popping back out of it again. We know these are measurable forces but what interests Feigel is the momentum associated with these electromagnetic fields. Learning how to manipulate that momentum could allow us to create a reaction we can use for propulsion. From the paper:

In this article we demonstrate that aggregating or rotating magneto-electric particles change[s] the momentum of [the] quantum vacuum and, as a consequence they acquire the resulting difference. It follows from momentum conservation: any change in momentum of zero fluctuations is compensated by a corresponding change in the momentum of a material object or electromagnetic field. These new occurrences of the vacuum momentum transfer do not require external means, such as previously proposed modification of the magneto-electric constant by applying external electric and magnetic fields or suppressing the quantum vacuum modes by cavity-imposed boundary conditions.

I don’t have the background to know whether what Feigel goes on to discuss is workable or not, but I do want to point you to the paper and the recent spate of comments on it. What I can do is farm Feigel’s work out to several Tau Zero practitioners whose expertise in the area of the quantum vacuum will allow them to make an informed judgment. Until then, let’s look at what Feigel says about what some are calling a ‘quantum propulsion machine.’

Feigel’s ‘magneto-electric quantum wheel’ would tap the forces in the quantum vacuum by introducing magneto-electric nanoparticles that would interact with them. Technology Review‘s physics arXiv blog discusses what Feigel is proposing:

The first method is to rapidly aggregate a number of magnetoelectric nanoparticles, a process which influences the boundary conditions for higher frequency electromagnetic waves, generating a force.

The second is simply to rotate a group of magnetoelectric nanoparticles, which also generates a Lorentz force.

Either way, the result is a change in velocity…

The magneto-electric quantum wheel would be what Feigel calls “…an addressable array of small magneto-electric particles or wires” which, upon rotation, would generate a force. Let me quote more fully from the paper:

…mechanical action of [the] quantum vacuum on magneto-electric objects may be observable and have a significant value. Rotation or self-assembly of the nanoparticles is enough to generate a back-action from zero electro-magnetic fluctuations. The amount of momentum that can be extracted from quantum vacuum by this effect may have in the future practical implications, depending on advances in magneto-electric materials.

The applications the author is talking about involve correcting the attitude of satellites in space. These are tiny effects, but the concept, which would involve propulsion that would occur without any loss of mass, is intriguing for that reason alone. Carrying propellant is a huge constraint as we look toward missions into deep space. Most of the vehicle is devoted to fuel tanks — consider Daedalus, or the ongoing Icarus project. Heck, consider Apollo, with its 600 to 1 mass ratio. Leaving the propellant at home is why concepts like Robert Forward’s lightsails can get to a star using known physics.

In the far future, what if we could harness the quantum vacuum to achieve significant propulsion without the huge mass ratio problem? We’re a long way from that, but if Feigel’s ideas are testable, let’s see where they may lead. I’ll hope to be posting further thoughts on this from Tau Zero practitioners soon. The paper is Feigel, “A magneto-electric quantum wheel,” available online.

tzf_img_post

Iapetus: Coated in Off-world Dust

Saturn’s moon Iapetus has always had an unusual aspect, one first noted all the way back in the days of Giovanni Cassini (1625-1712), for whom our Saturn orbiter is named. The moon’s discoverer, Cassini correctly noted that Iapetus had a bright hemisphere and a dark one, each visible (because of tidal lock) on only one side of the planet as viewed from Earth. We now call the dark hemisphere Cassini Regio in honor of the Italian-born astronomer.

SaturnMoonLarge

Image: Cassini-Huygens spacecraft images of Iapetus’ dark, leading side and its bright, trailing side. The high-resolution images shed new light on the long-standing puzzle of how Iapetus got its unusual coloration. Credit: Cassini Imaging Team.

So what makes Cassini Regio so dark? Interior activity on the moon itself is one possibility, but the leading theory is that dusty debris from Saturn’s moon Phoebe is the source. Now images from the Cassini orbiter have been analyzed, with a paper in Science concluding that Cassini Regio is being bombarded by debris from Phoebe. The images can show impact craters down to a resolution on the order of 10 meters to the pixel. Small bright craters are found within the dark hemisphere that indicate the dark surface material is likely only a few meters thick. Moreover, both dark and bright materials on the leading side are much redder in color than on the trailing side.

The leading side’s dust, in other words, seems to have come from somewhere else. Moreover, the transition from dark to light hemisphere is shown to be not a solid line but a mottled array of dark and light spots. Couple this with recent work in Nature that announced the discovery of an enormous ring of debris ten thousand times the area of the main ring system, around Saturn and near Phoebe, a system that supports the dust from Phoebe hypothesis. It is thought that impacts on Phoebe keep the ring supplied with material, and that this material then migrates inward to strike the dark side of Iapetus.

Joseph Burns (Cornell University) thinks the dust question has been resolved:

“The ring of collisional debris that has come off Phoebe is out there, and its companion moons are out there, and now we understand the process whereby the stuff is coming in. When you see the coating pattern on Iapetus, you know you’ve got the right mechanism for producing it.”

Remember that Iapetus is hardly alone when it comes to dark material being found on the surface. Not long ago we looked at studies showing black coatings on Hyperion, Dione and Phoebe as well, suggesting a common mechanism for carrying the material from one moon to another. That work was intriguing because there’s some evidence for geological activity on Dione, but evidently not enough to serve as the source for its dark materials. Here I’m going to repeat a quote I used earlier from Cassini scientist Bonnie Buratti:

“Ecology is about your entire environment — not just one body, but how they all interact. The Saturn system is really interesting, and if you look at the surfaces of the moons, they seem to be altered in ways that aren’t intrinsic to them. There seems to be some transport in this system.”

Indeed, and with Cassini’s help we’re untangling its mysteries. The paper is Denk et al., “Iapetus: Unique Surface Properties and a Global Color Dichotomy from Cassini Imaging,” published online in Science on 10 December, 2009 (abstract). The paper on the ring discovery is Verbiscer et al, “Saturn’s largest ring,” Nature 461, (22 October 2009), pp. 1098-1100 (abstract).

tzf_img_post

WISE Launch Again Rescheduled

Launch of the WISE mission has again been delayed, now scheduled for December 14 with a launch window of 1409 to 1423 UTC (0909-0923 EST). Launch will take place at Vandenberg Air Force Base in California, with coverage offered on NASA TV. A live feed from the on-board camera will be active here.

The Wide-field Infrared Explorer will spend nine months covering the entire sky at mid-infrared wavelengths, studying targets ranging from the remotest galaxies to near-Earth objects, and building our catalog of brown dwarfs near the Sun. Most infrared wavelengths can’t penetrate Earth’s atmosphere, so a space-based perch — WISE will take up a circular polar orbit some 525 kilometers up — is essential for good viewing. The complete WISE survey will involve over a million images, forming a source catalog for the James Webb Space Telescope, which is scheduled for a 2014 launch.

wise20091209

Image: The Wide-field Infrared Survey Explorer mission will survey the entire sky in a portion of the electromagnetic spectrum called the mid-infrared with far greater sensitivity than any previous mission or program ever has. The survey will consist of over a million images, from which hundreds of millions of astronomical objects will be catalogued, providing a vast storehouse of knowledge about the solar system, the Milky Way, and the universe. Credit: NASA/JPL.

The catalog idea is an important one. All-sky surveys, in this case at wavelengths from 3.5 to 23 microns, make for the most efficient use of large telescopes by building the target list for detailed investigation. The brown dwarf issue is especially intriguing because WISE should be able to tell us much about their distribution in nearby space, including the ever interesting question of whether any brown dwarfs exist closer to us than the Centauri stars. Because brown dwarfs can have planetary systems of their own, a dwarf like this would be an obvious candidate for future deep-space probes.

We’ve had surveys working in the infrared before, including the Two Micron All-Sky Survey (2MASS), a ground-based study that covered the sky in the near-infrared (between 1.25 and 2.17 microns) and the Cosmic Background Explorer (COBE), a space-based mission that worked at infrared and microwave wavelengths (its infrared range was 1.25 to 3.5 microns). And then there was IRAS, the Infrared Astronomical Satellite of the 1980’s, working between 12 and 100 microns. The mid-infrared, in other words, represents a gap in current data that WISE will fill.

Moreover, says principal investigator Ned Wright (UCLA), WISE should seriously ramp up the quality of our data, because previous surveys worked with less sensitive detectors — IRAS, for example, used just 62 pixels to cover four infrared bands, while WISE can work with four million pixels. In the wavelength range where the surveys overlap, WISE will offer hundreds of times the sensitivity of IRAS and hundreds of thousands of times that of COBE. “The old all-sky infrared pictures were like impressionist paintings,” says Wright. “Now, we’ll have images that look like actual photographs.”

Current thinking is that there may be as many brown dwarfs as normal stars in the galaxy. But WISE will also be useful at pinpointing near-Earth objects such as asteroids and comets, and if we really get lucky, we may find something intriguing in the Oort Cloud. This Space.com article, for example, speculates that a gas giant the size of Neptune or even Jupiter could lurk among the comets there, throwing yet another monkey wrench into our definition of a planet. At the other end of the distance scale, WISE will look at the earliest galaxies in formation, dust-shrouded objects laden with new stars that are all but impossible to study in visible light.

tzf_img_post