Astrometry Bags a ‘Cold Jupiter’

We’re now up to 347 detected exoplanets around 293 stars. The latest find turns out to be intriguing on several counts. VB 10 is a red dwarf about 20 light years away in the constellation Aquila. Its newly detected planet is a gas giant with a mass six times that of Jupiter, a ‘cold Jupiter’ not so different from our own. Interestingly, although the star is considerably more massive, both planet and star should have roughly the same diameter.


Image: This artist’s diagram compares our solar system (below) to the VB 10 star system. Astronomers successfully used the astrometry planet-hunting method for the first time to discover a gas planet, called VB 10b, around a very tiny star, VB 10. All of the bodies in this diagram are shown in circular insets at the same relative scales. Astrometry involves measuring the wobble of a star on the sky, caused by an unseen planet yanking it back and forth. Because the VB 10b planet is so big relative to its star, it really tugs the star around. The red circle seen at the center of the VB 10 system shows just how big this wobble is. Because our sun is more massive than VB 10, its planets do not cause it to wobble nearly as much. Credit: NASA/JPL-Caltech

With a mass just one-twelfth that of the Sun, VB 10 is truly a tiny star, about one-tenth the size of ours, and one that now holds the record for the smallest star known to host a planet. But VB 10b raises the eyebrows for other reasons, not the least of which is that it is found in such an intriguing orbit. Here’s Steven Pravdo (JPL), lead author of the study on this world:

“We found a Jupiter-like planet at around the same relative place as our Jupiter, only around a much smaller star. It’s possible this star also has inner rocky planets. And since more than seven out of 10 stars are small like this one, this could mean planets are more common than we thought.”

More good news, then, for the M-dwarf contingent, among which I count myself an enthusiastic member. The gas giant here actually orbits every nine months at a distance similar to Mercury’s spacing from the Sun (fifty million kilometers). Inner, rocky planets could exist in this star’s habitable zone. But despite the effects of tidal lock, there is continuing speculation that temperate conditions could exist on such worlds.

So does VB 10 actually house a solar system not so different from our own? We don’t know, but what does become apparent is that any techniques that help us find ‘cold Jupiters’ (as opposed to the ‘hot Jupiters’ so prevalent because of selection effects in our early results) will help us turn up more systems arranged something like ours.

The other noteworthy aspect of this work is that the observations, made at the Palomar Observatory near San Diego, flagged the star by means of astrometry. Unlike radial velocity studies, which look at the Doppler shifts in starlight as a star is pulled toward and then away from us by a planet, astrometry detects the tiniest of changes in the positions of stars in the sky. VB 10b becomes the first exoplanet found using astrometry, a method Pravdo calls “…optimal for finding solar-system configurations like ours that might harbor other Earths.” More in this JPL news release.

Radio Supernovae and the ATA

We think of the Allen Telescope Array, currently comprising only 42 of the 350 radio dishes planned, as a SETI instrument, capable of digging faint signals out of a wider field of stars than ever before. But the ATA is also engaged in an astrophysical survey of the sky at radio wavelengths, one that will look for radio bursts from supernovae. A glimpse of what it is looking for has just been reported in M82, a small irregular galaxy about twelve million light years from Earth.

We’re talking about a so-called ‘radio supernova,’ an exploding star undetectable by optical or X-ray telescopes. The new object is the brightest supernova seen in radio wavelengths in the last twenty years, and one of only a few dozen of its kind observed so far. And while the ATA will help us locate future radio objects of its kind, this one was found with the Very Large Array in New Mexico, and later confirmed through the NRAO’s Very Long Baseline Array.


Image (click to enlarge): Zooming into the center of the galaxy M82, one of the nearest starburst galaxies at a distance of only 12 Million light years. The left image, taken with the Hubble Space Telescope (HST), shows the body of the galaxy in blue and hydrogen gas breaking out from the central starburst in red. The VLA image (top left) clearly shows the supernova (SN 2008iz), taken in May 2008. The high-resolution VLBI images (lower right) shows an expanding shell at the scale of a few light days and proves the transient source as the result of a supernova explosion in M82. Credit: Milde Science Communication, HST Image: /NASA, ESA, and The Hubble Heritage Team (STScI/AURA); Radio Images: A. Brunthaler, MPIfR.

Both the VLA and the VLBA have narrow fields of view, but the ATA will offer full-sky scanning on a daily basis, and will be able to find objects ten times fainter than this radio supernova. In the process, we’ll learn much about how radio supernovae work even as we continue the hunt for life around other stars. All of this should bring a more cohesive approach to the study of these objects, says Geoffrey Bower (UC-Berkeley):

“This supernova is the nearest supernova in five years, yet is completely obscured in optical, ultraviolet and X-rays due to the dense medium of the galaxy. This just popped out; in the future, we want to go from discovery of radio supernovas by accident to specifically looking for them.”

A supernova can produce radio emissions when it’s found in an active region of star formation, where the density of gas and dust is high — that very gas and dust is, of course, the reason why it is so hard to detect these objects in optical, ultraviolet and X-ray wavelengths. Those supernovae that have not lost large parts of their envelope before collapsing to form a neutron star or black hole produce few radio emissions.

The team has found indications of a ring structure produced by a shock wave around this object, one that has grown to about 2000 AU across and is consistent with a year-old supernova. Astronomers hope the emissions from these objects will offer up information about how stars explode and how their cores collapse. Debris colliding with the stellar wind should provide rich data to observers, while the ATA’s ongoing survey should take us deep into the realm of transient and variable sources.

The paper is Brunthaler et al., “Discovery of a bright radio transient in M82: a new radio supernova?,” accepted at Astronomy & Astrophysics and available online. More in this news release from the Max-Planck-Institut für Radioastronomie.

Maps of an Alien Earth

Anyone who thought the Deep Impact mission was over when the spacecraft drove an impactor into comet Tempel 1 some four years ago has been given a lesson in the strategy of extended missions. Now heading for a flyby of comet Hartley 2 (late in 2010), Deep Impact is also doing yeoman work in the study of extrasolar planets. That phase of the mission is called Extrasolar Planet Observations and Characterization (EPOCh), but the spacecraft housing both investigations is now referred to as EPOXI.

If the acronyms can be confusing, the latest news from EPOXI is straightforward, and encouraging. A paper slated for summer publication in the Astrophysical Journal reports on the spacecraft’s observations of our own planet, made in 2008 when it was between 17 and 33 million miles from Earth. The idea was to tune up our capabilities at observing distant planets, using spectral information to map the distribution of continents and oceans. EPOXI’s High Resolution Imager thus set up a trial of Earth’s changing light as the planet rotates.


Image: Top panel: a normal map of Earth, made by earthlings who live here. Lower panel: An “Alien Map” of Earth, made from the EPOXI data after collapsing it to a single pixel. This is the kind of map that we should be able to make for Earth-like extrasolar planets, to reveal that they have oceans and continents like our home world. Credit: NASA/Drake Deming.

EPOXI studied Earth’s light in two separate 24-hour observational periods covering seven bands of visible light. Small deviations in the average color caused by surface features and clouds rotating in and out of view displayed two dominant colors, one reflective at red wavelengths, the other at shorter blue wavelengths. Mapping the changes over the 24-hour period allowed the scientists to compare what they were seeing with Earth’s actual oceans and continents. The upshot: It should be possible to pick out oceans on distant exoplanets.

The technique will obviously be superseded by future space instruments, but what the researchers have found is usable and could aid in the construction of later telescopes. Says Drake Deming (NASA GSFC and a co-author of the paper):

“A spectrum of the planet’s light that reveals the presence of water is necessary to confirm the existence of oceans. Finding the water molecule in the spectrum of an extrasolar planet would indicate that there is water vapor in its atmosphere, making it likely that the blue patches we were seeing as it rotates were indeed oceans of liquid water. However, it will take future large space telescopes to get a precise spectrum of such distant planets, while our technique can be used now as an indication that they could have oceans.”


It’s worth pointing out that the maps flowing out of the EPOXI data are sensitive only to the East-West positions of oceans and continents, and the data were taken when the spacecraft was directly above the equator. That, says Nicolas Cowan (University of Washington), sets up an inherent limitation in terms of viewing geometry. “We could erroneously see the planet as a desert world if it had a nearly solid band of continents around its equator and oceans at its poles.”

Image: the Earth-Moon system is seen with the Moon beginning its transit in front of Earth. It was taken on May 29, 2008 through three filters: blue, green and orange, centered at 450, 550 and 650 nm respectively, while the spacecraft was 0.33 AU (49,367,340 km and 30,675,43 miles) from Earth. Credit: NASA/JPL-Caltech/UMD/GSFC.

The things you can do by massaging a few pixels! Finding liquid water on an extrasolar planet in the habitable zone of its star would tell us we had located a potentially living world. Now it’s a matter of getting next-generation instruments into space that can return actual images of planets as small as Earth. When we have them in position, the varying light of that pale blue dot could be our first indication of success at finding an analog to our planet.

The paper is Cowan et al., “Alien Maps of an Ocean-Bearing World,” accepted for publication in the Astrophysical Journal and available online.

Growing the Interstellar Probe

Centauri Dreams reader Brian Koester passed along a link to a provocative video last month that spurs thoughts about the nature of interstellar probes. The video is a TED talk delivered by Paul Rothemund in 2007. For those not familiar with it, TED stands for Technology, Entertainment, Design, a conference that began in 1984 and now brings together interesting scientific figures whose challenge is to give the best talk they can on their specialty within the span of eighteen minutes.

I’ve been pondering Rothemund’s talk for some time. You can call this Caltech bioengineer a ‘DNA origamist,’ meaning that he is exploring ways to fold DNA into shapes and patterns. As becomes clear in his presentation, folding DNA into ‘smiley’ faces or maps has a certain wow factor, but once you get past the initial wonder of working at this level, you begin to appreciate how research in DNA nanotechnology points toward self-assembling devices that can be built at the micro-scale.

Molecular Computing to the Stars

And now we’re off to the races, for as Koester noted in his email to me, a small interstellar probe could theoretically create a molecular computer which could then, upon arrival, create electronic equipment of the sort needed for observations. Think of a probe that gets around the payload mass problem by using molecular processes to create cameras and imaging systems not by mechanical nanotech but by inherently biological methods.

A Von Neumann self-replicating probe comes to mind, but we may not have to go to that level in our earliest iterations. The biggest challenge to our interstellar ambitions is propulsion, with the need to push a payload sufficient to conduct a science mission to speeds up to an appreciable percentage of lightspeed. The more we reduce payload size, the more feasible some missions become — Koester was motivated to write by considering ‘Sundiver’ mission strategies coupled with microwave beaming.

The question becomes whether molecular computing can proceed to develop the needed instrumentation largely by tapping resources in the destination system, a process John Von Neumann called ‘interstellar in-situ resource utilization.’ The more in-system resources we can tap (in the destination system, that is), the lighter our initial payload has to be, and yes, that raises countless issues about targeting the mission and the flexibility of the design once arrived to conduct the needed harvesting.

Toward Self-Replication?

What an interesting concept. It’s fascinating to see how far the notion of self-replication has taken us since Robert Freitas produced a self-replicating interstellar probe based on the original Project Daedalus design. That one, called REPRO, would mine the atmosphere of Jupiter for helium-3, just like Daedalus, and would use inertial confinement fusion for propulsion. But REPRO would carry a so-called SEED payload that, upon arrival on the moon of a gas giant, would produce an automated factory that would turn out a new REPRO every five hundred years.

But REPRO would have been massive (each SEED payload would weigh in at close to five hundred tons), with all the challenges that added to the propulsion question. Freitas later turned to nanotech ideas in advocating a probe more or less the size of a sewing needle, with a millimeter-wide body and enough nanotechnology onboard to activate assemblers on the surface of whatever object it happened to find in the destination system.

Now we’re looking at a biological variant of this concept that could, if extended, be turned to self-replication. Rothemund says that he wants to write molecular programs that can build technology. A probe built along these lines could use local materials to create the kind of macro-scale objects needed to form a research station around another star, the kind of equipment we once envisioned boosting all the light years to our target. How much simpler if we can build the needed tools when we arrive?

A Long Leap for DNA Origami

Caltech’s Erik Winfree, who works with Rothemund, gave New Scientist a recent update on where the work stands:

Although the team has so far used the technique to build simple pipes… much more is possible, Winfree says. “Metaphorically, this is similar to how genetic programs within cells direct the growth of an organism.”

Winfree and Rothemund speculate that the technique could provide a way to assemble molecular components into useful structures such as tiny electric circuits. It is also possible to use the self-assembling DNA structures to perform computational tasks, adds Winfree.

“It is very powerful for information processing,” he says. “It’s what’s known as a Universal Turing Machine, which means it can carry out any information processing task.”

Can the method ultimately be extended to serve our interstellar purpose? You can get an overview of Paul Rothemund’s work from the video I linked to above, and also in his paper “Folding DNA to create nanoscale shapes and patterns,” Nature Vol 440 (16 March 2006), pp. 297-302 (available online). Publications from Caltech’s DNA and Natural Algorithms Group are available here.

Finally, on the question of assembly and replication, see Barish et al., “An information-bearing seed for nucleating algorithmic self-assembly,” Proceedings of the National Academy of Sciences Vol. 106, No. 15, pp. 6054-6059 (available online).

Creating Stars in the Laboratory

The 192 lasers of the National Ignition Facility at Lawrence Livermore National Laboratory in California can focus 500 trillion watts of power onto a pellet of hydrogen fuel the size of a pencil eraser. With full-scale experiments slated to begin soon, we’ll learn much about the feasibility of nuclear fusion on Earth, hoping to extract more energy from the process than goes into making it happen. The forms of hydrogen at play here are deuterium and tritium, which fuse to form helium.


Image: All of the energy of NIF’s 192 beams is directed inside a gold cylinder called a hohlraum, which is about the size of a dime. A tiny capsule inside the hohlraum contains atoms of deuterium (hydrogen with one neutron) and tritium (hydrogen with two neutrons) that fuel the ignition process. Credit: National Ignition Facility.

Inertial confinement fusion using lasers is a different approach than the magnetic confinement method used at the International Thermonuclear Experimental Reactor (ITER), currently being built in Cadarache, France. There, super-heated gas is managed via magnetic fields inside a vessel called a tokamak.

But as multi-track fusion studies continue, it’s interesting to see how the National Ignition Facility will also serve as a laboratory for astronomers hoping to understand the physics of exploding stars. At full power, the NIF lasers will throw a 1.8 megajoule punch at the target. Energies like this, according to a recent BBC story on the NIF, will create temperatures of 100 million degrees and pressures billions of times greater than Earth’s atmospheric pressure, forcing hydrogen nuclei to fuse.

But adjusting the elements in the fuel pellet also sets up experiments that mimic a stellar core. The result is a mini-supernova, says Paul Drake (University of Michigan):

“You choose the material and the structures between them to be relevant to what happens when the star explodes. The laser would strike the centre – the analogue of the core of the star – launching a tremendously strong shock wave that would blow the material apart.”

All this occurs, of course, in billionths of a second, so that the results have to be scaled to the actual astrophysical environment. Nonetheless, ‘supernova’ experiments like these could be productive in helping us understand the stellar explosions that produced the elements so crucial for life. That adds a powerful tool to our arsenal, complementing the observing programs that search for supernovae in distant galaxies.

The BBC also talks to David Stevenson (Caltech) about using the NIF to study the formation of gas giant planets. Because the NIF’s lasers can produce pressures equivalent to billions of times what is found at sea level on Earth, we can study conditions that exist inside such planets, where dramatic changes to chemistry occur. The behavior of hydrogen, helium, carbon and water in such a setting should be fascinating.

We already know that hydrogen can become a metallic fluid at much lower pressures. Ray Jeanloz (UC – Berkeley) paints a graphic picture of such materials in a Jupiter-like setting:

“Hydrocarbons would actually decompose to a mixture of hydrogen and a carbon. The end result being that diamonds would actually be hailing out of the atmosphere. That’s the kind of process you would never have guessed unless you had studied the materials themselves.”

The National Ignition Facility will be the world’s largest and highest-energy laser system, delivering more than sixty times the energy of any previous laser facility. But keep your eye as well on the European High Power Laser Energy Research (HIPER) study, which received a funding boost last October. Construction of HIPER isn’t scheduled to begin for a decade or so, but success at NIF could be followed by a HIPER facility aimed at taking inertial confinement fusion to a truly commercial level.