by Paul Gilster | Jun 2, 2015 | Exoplanetary Science |
The Scorpius-Centaurus OB association is a collection of several hundred O and B-class stars some 470 light years from the Sun. Although the stars are not gravitationally bound, they are roughly the same age — 10 to 20 million years — their formation triggered by a series of supernovae explosions in large molecular clouds. Now the Gemini Planet Imager on the Gemini South instrument in Chile has uncovered a young planetary system within the association, one with solid similarities to our own Solar System in its infancy.
In fact, says lead author Thayne Currie (Subaru Telescope), the ring orbiting the star HD 115600 could be a Solar System clone. “It’s kind of like looking at [our] outer solar system when it was a toddler,” the astronomer adds, noting that the ring is about the same distance from its host star as the Kuiper Belt is from the Sun, receiving about the same amount of light from an F-class star that is about fifty percent more massive than our own G-class Sol.
Image: The F-class star HD 115600 showing a bright debris ring viewed nearly edge-on and located just beyond a Pluto-like distance to its star. One or more unseen planets are causing the disk center to be offset from the star’s position (cross). Credit: Thayne Currie/NAOJ.
Distortions in the observed debris disk indicate that it is interacting with at least one thus far unseen planet, creating an eccentricity in the disk itself that is among the largest yet observed. A gas giant of Jupiter or Saturn class could explain the distortions, but there are also other possibilities depending on the models used — the researchers explored ‘gap opening’ models as well as ‘planet stirring’ explanations. From the paper:
Interior to ? 30 AU only a superjovian-mass planet can sculpt the ring by gap opening… Planets with masses and semimajor axes comparable to the outer solar system planets could stir the disk to appear as a bright debris ring with an eccentricity of 0.1–0.2 (e.g. a Saturn with e = 0.2). In both cases, Super-Earths just interior to the ring edge could sculpt the ring.
So we have a range of planetary possibilities here amidst a disk whose spectrum shows similarities to the Kuiper Belt, with a composition of ice, silicates and dust, although the researchers note that HD 115600’s disk is, in comparison with other debris disks, more efficient at scattering starlight, implying a higher percentage of ices:
HD 115600’s disk is reflecting light more efficiently than HR 4796A’s disk while having less thermal emission, a result explicable if HD 115600s disk is dominated by higher albedo species like water-ice. Multi-wavelength photometry/spectroscopy is needed to more decisively assess the composition of HD 115600’s disk.
Even so, it’s clear that HD 115600 is a promising source for further information about the early development of disks like the Kuiper Belt, with clear evidence for the sculpting effects of at least one planet. This work was conducted with the Gemini Planet Imager, a new generation of adaptive optics instruments whose numbers are soon to grow. The HD 115600 system thus becomes a useful reference as we tighten our focus on planet-disk interactions.
The paper is Currie et al., “Direct Imaging and Spectroscopy of a Young Extrasolar Kuiper Belt in the Nearest OB Association,” in press at The Astrophysical Journal Letters (preprint). A Subaru Telescope news release is available.
by Paul Gilster | Jun 1, 2015 | Sail Concepts |
It was a worrisome eight days, but LightSail has broken its silence with an evident reboot and return to operations, sending telemetry to ground stations and taking test images. We now have sail deployment possibly as early as Tuesday morning EDT (15:44 UTC), but according to The Planetary Society’s Jason Davis, much will depend on today’s intensive checkout.
Planetary Society CEO Bill Nye issued this statement on the spacecraft’s reawakening:
“Our LightSail spacecraft has rebooted itself, just as our engineers predicted. Everyone is delighted. We were ready for three more weeks of anxiety. In this meantime, the team has coded a software patch ready to upload. After we are confident in the data packets regarding our orbit, we will make decisions about uploading the patch and deploying our sails— and we’ll make that decision very soon. This has been a rollercoaster for us down here on Earth, all the while our capable little spacecraft has been on orbit going about its business. In the coming two days, we will have more news, and I am hopeful now that it will be very good.”
Image: LightSail-A back in August of 2014 during a testing period at Cal Poly. The craft is a three-unit CubeSat no larger than a loaf of bread, but it packs 32 square meters of sail inside. Four metal booms will, if all goes well, unfold the craft’s four triangular sails. Credit: The Planetary Society.
What we get from Davis is largely positive (see LightSail Team Prepares for Possible Tuesday Sail Deployment). The diminutive craft made twelve passes over the Cal Poly and Georgia Tech ground stations on Sunday, returning 102 data packets. You’ll recall that errant software was suspected in LightSail’s problems, with engineers crafting a software patch that they tried unsuccessfully to upload. The trick is that the satellite is tumbling, able to receive some commands and transmit data, but lacking the kind of stable downlink that would allow the software changes to be made. For that reason, the patch idea is now being abandoned.
Instead, a series of reboots will keep the beacon.csv file reset so that it doesn’t fill up and crash the system. Understandably, the LightSail team wants to begin sail deployment as soon as it is safe to do so. We should have a final decision on a possible Tuesday deployment by Monday night. We’re going to find out what effect the spacecraft’s tumble has on sail deployment the hard way. As Davis noted in an earlier post:
… the rotation rate has increased from -7, -0.1 and -0.3 degrees per second about the X, Y, and Z axes to 10.8, -7.3 and 2.9 degrees. The cause for the tumbling uptick currently unknown, but with the spacecraft’s attitude control system offline [see What Images Will We Get Back from the LightSail Test Mission?], sail deployment is likely to be a wild ride.
The best Tuesday ground pass window begins at 11:44 EDT. To keep up with the latest, follow Jason’s Twitter account @jasonrdavis, and we’ll see just how wild a ride it is. Remember, this mission is not designed to demonstrate controlled solar sailing, but serves as a test of the craft’s attitude control system and sail systems before it is pulled back into the Earth’s atmosphere. The tumbling we’re seeing now is obviously a concern because just next year the next LightSail mission is scheduled to perform controlled Earth-orbit sail flight. We’re going to need to find the bugs in this spacecraft’s attitude control system long before then.
