by Paul Gilster | Jun 14, 2019 | Exoplanetary Science |
We’re getting first results from the Gemini Planet Imager Exoplanet Survey (GPIES), a four-year look at 531 young, nearby stars that relies on the instrument’s capabilities at direct imaging. Data from the first 300 stars have been published in The Astronomical Journal, representing the most sensitive, and certainly the largest direct imaging survey for giant planets yet attempted. The results of the statistical analysis are telling: They suggest that planets slightly more massive than Jupiter in outer orbits around stars the size of the Sun are rare.
The Gemini Planet Imager (GPI), located at the Gemini South Telescope in Chile, can achieve high contrast at small angular separations, making it possible to see exoplanets directly, as opposed to the indirect methods that have dominated the field, such as transits and radial velocity analysis. As successful as the latter have been, they are most effective with planets closer to their stars, whereas an instrument like the GPI can find planets in regions outside the orbit of Jupiter. The GPI can directly image exoplanets a millionth as bright as the host star.
Bruce Macintosh (Stanford University), principal investigator for the GPI, calls this effort “…the most sensitive direct imaging survey for giant planets published to date.” The question it raises is significant: Just how representative is our Solar System in having gas giants like Jupiter and Saturn in outer orbits around a G-class star? We’re only beginning to learn the answer, but surveys like this one are on track to tell us. The answer may have astrobiological consequences, as Franck Marchis (SETI Institute), a co-author of the just published report, explains:
“We suspect that in our solar system Jupiter and Saturn sculpted the final architecture that influences the properties of terrestrial planets such as Mars and Earth, including basic elements for life such as the delivery of water, and the impact rates. A planetary system with only terrestrial planets and no giant planets will probably be very different to ours, and this could have consequences on the possibility for the existence of life elsewhere in our galaxy.”
Image: Close-up Picture of Gemini Planet Imager currently located at Gemini South Observatory in Cerro Pachon. Photo by J. Chilcote.
Out of the 300 stars in the thus far released Gemini survey data, 123 are more than one-and-a-half times more massive than the Sun. What the data show is that the hosts of the planets thus far detected are all among the higher mass stars. This despite the fact that given the differential between stellar light and that of a planet, a giant planet orbiting a fainter star more like the Sun is actually easier to see. This relationship of mass to giant planet frequency has been discussed in the literature and is now strengthened by the results of the GPI survey.
The results of the Gemini survey pick up on the theme that other planetary systems tend to be different from our own, despite the assumption that gas giants in outer orbits and rocky worlds on inner orbits would be a fairly standard pattern. Both the GPIES and other exoplanet surveys point to the rarity of giant planets around stars as small as the Sun. Worlds several times more massive than Jupiter and above (the GPIES is not sensitive enough to pick up planets of as low a mass as Jupiter itself) tend to be hosted by stars more massive than the Sun. Our own wide-orbit Jupiter, then, may be a statistical outlier, although that is yet to be determined.
From the paper’s conclusion:
From the first 300 stars observed out of the planned 600-star survey, reaching contrasts of 106 within 1?? radius, GPIES is one of the largest and deepest direct imaging surveys for exoplanets conducted to date. Our analysis of the data shows that there is a clear stellar mass dependence on planet occurrence rate, with stars >1.5 M? [i.e. 1.5 times Solar mass] more likely to host giant planets (5–13 MJup ) at wide separations (semimajor axes 10–100 au) than lower-mass stars.
The paper reports the imaging of six planets and three brown dwarfs, with a sensitivity to planets of several Jupiter masses at orbital distances comparable to those beyond Saturn (at least 12 gas giants had been expected based on earlier models). The only previously unknown planet was 51 Eridani b, which was discovered via GPI as far back as 2014, a gas giant of two-and-a-half Jupiter masses in a Saturn-like orbit around a young star some 97 light years away, and one that had been previously unknown despite attempts to observe the star because no other instrument was able to sufficiently suppress the starlight to make the planet visible.
Image: Results of the survey of 531 stars and their exoplanets in the southern sky are plotted to indicate their distance from Earth. Gray dots are stars without exoplanets or a dust disk; red are stars with a dust disk but no planets; blue stars have planets. Dots with rings indicated stars imaged multiple times. Credit: Paul Kalas, UC Berkeley; Dmitry Savransky, Cornell; Robert De Rosa, Stanford.
Another useful find: A brown dwarf labeled HR 2562 B, 30 times more massive than Jupiter in a Uranus-like orbit. This brown dwarf and the other two imaged in the study shed light on planet vs. brown dwarf formation at wide separations from the host star. The question of brown dwarf vs. planet formation is long-standing. Whereas stars have been considered to form through the gravitational collapse of large clouds of gas and dust, planets are thought to have formed largely through core accretion, as small rocky bodies undergo collision and accumulation of mass.
Eugene Chiang (UC-Berkeley) is a co-author of the paper:
“What the GPIES Team’s analysis shows is that the properties of brown dwarfs and giant planets run completely counter to each other. Whereas more massive brown dwarfs outnumber less massive brown dwarfs, for giant planets, the trend is reversed: less massive planets outnumber more massive ones. Moreover, brown dwarfs tend to be found far from their host stars, while giant planets concentrate closer in. These opposing trends point to brown dwarfs forming top-down, and giant planets forming bottom-up.”
So our Solar System evidently doesn’t resemble many other systems that we’ve observed. Gas giants in outer orbits seem to be more common around significantly larger stars. Putting together a catalog of gas giants in the outer systems of other neighboring stars is going to take time — it’s telling that even the GPI can’t detect Jupiter-mass planets in these orbits — but the GPIES is the beginning of that process, and one that will soon publish additional results. Observations in the survey wrapped up in January with an examination of its 531st star. Moving toward their report on the complete dataset, the team is now following up candidate planets at the same time that it begins an upgrade on the Gemini Planet Imager itself.
The paper is Nielsen et al., ”The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au,” Astronomical Journal Vol. 158, No. 1 (12 June 2019). Abstract.
by Paul Gilster | Jun 13, 2019 | Outer Solar System |
We have priceless data on Europa from the Voyager and Galileo missions, but we’re updating earlier interpretations thanks to new work with both the Hubble Space Telescope and the Keck Observatory on Mauna Kea (Hawaii). Thus the discovery that the yellow color visible on parts of Europa’s surface in visible light is most likely sodium chloride (NaCl), familiar as table salt and the principal component of sea salt. That’s an interesting result, given that it suggests a Europan ocean chemically more similar to Earth’s than we had previously assumed.
The re-thinking of the spacecraft data stems from the fact that Galileo was equipped with the Near-Infrared Mapping Spectrometer instrument, useful for analyzing the surface of a planetary body. What Galileo lacked, however, was a visible spectrometer to complement its near-infrared device. The problem: Chlorides are not apparent in the near-infrared. While Galileo had found water ice, it identified a substance believed to be magnesium sulfate salts on the surface.
But spectral data from the Keck instrument showed none of the expected sulfate absorptions. Caltech graduate student Samantha Trumbo is lead author of the paper on this work:
“No one has taken visible-wavelength spectra of Europa before that had this sort of spatial and spectral resolution. The Galileo spacecraft didn’t have a visible spectrometer. It just had a near-infrared spectrometer, and in the near-infrared, chlorides are featureless.”
The researchers used spectra obtained with the Hubble instrument to detect a 450-nm absorption indicating irradiated sodium chloride on the surface. Moreover, this feature correlates with the interesting ‘chaos’ terrain that seems to show interactions with the ocean below, making it appear that there is an interior source for the sodium chloride, as discussed in the paper’s conclusion:
As chaos terrain is geologically young, extensively disrupted, and potentially indicative of locations of subsurface upwelling or melt-through…, and as the leading hemisphere chaos regions are shielded from the sulfur implantation of the trailing hemisphere, the composition of these regions may best represent that of Europa’s endogenous material. However, their spectra are categorically smooth at higher spectral resolution, lacking any identifiable infrared spectral features other than those of water ice. Nevertheless, the unique geology and 1.5- to 4-μm spectra of leading hemisphere chaos terrain suggest a salty composition. Chloride salts provide a potential explanation…
At the Jet Propulsion Laboratory, co-author Kevin Hand put ocean salts to the test under conditions of radiation similar to Europa’s, finding that sodium chloride produced color changes under irradiation that could be identified through analysis of the visible spectrum. Hand likens the substance to invisible ink — radiation is what makes it apparent to the observer. In the laboratory, it turns a shade of yellow similar to the Europan region known as ‘Tara Regio.’ The 450-nm absorption in the visible spectrum detected by Hubble matches the irradiated salt in the laboratory, firming up the idea that Tara Regio’s color comes from irradiated NaCl.
Image: This color composite view combines violet, green, and infrared images of Jupiter’s intriguing moon, Europa, for a view of the moon in natural color (left) and in enhanced color designed to bring out subtle color differences in the surface (right). The bright white and bluish part of Europa’s surface is composed mostly of water ice, with very few non-ice materials. In contrast, the brownish mottled regions on the right side of the image may be covered by hydrated salts and an unknown red component. The yellowish mottled terrain on the left side of the image is caused by some other unknown component. Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers long. Credit: NASA/JPL/University of Arizona.
We could be looking at sodium chloride as one of the various materials found in the moon’s outer shell, but the prospect that it is derived from the subsurface ocean means that we may have an insight here into the chemistry going on beneath the ice. From the paper:
The presence of NaCl on Europa has important implications for our understanding of the internal chemistry and its geochemical evolution through time. Whereas aqueous differentiation of chondritic material and long-term leaching from a chondritic seafloor can result in a system rich in sulfates, more extensive hydrothermal circulation, as on Earth, may lead to an NaCl-rich ocean. The plume chemistry of Enceladus, which is perhaps the best analog to Europa, suggests an NaCl-dominated ocean and a hydrothermally active seafloor. However, the compositional relationship between Europa’s ocean and its endogenous material is unknown, and the surface may simply represent the end result of a compositional stratification within the ice shell… Regardless of whether the observed NaCl directly relates to the ocean composition, its presence warrants a reevaluation of our understanding of the geochemistry of Europa.
Image: In a laboratory simulating conditions on Jupiter’s moon Europa at NASA’s Jet Propulsion Laboratory in Pasadena, California, plain white table salt (sodium chloride) turned yellow (visible in a small well at the center of this photograph). The color is significant because scientists can now deduce that the yellow color previously observed on portions of the surface of Europa is actually sodium chloride. The JPL lab experiments matched temperature, pressure and electron radiation conditions at Europa’s surface. Credit: NASA/JPL-Caltech.
A more active seafloor than we have assumed? If so, Europan geology becomes still more interesting. A geologically young icy shell with striking areas showing past activity amid evidence of NaCl makes the assumption that these salts derived from the ocean plausible.
The paper is Trumbo et al., “Sodium chloride on the surface of Europa,” Science Advances Vol. 5, No. 6 (12 June 2019). Full text.
by Paul Gilster | Jun 12, 2019 | Exoplanetary Science |
We’re on the cusp of exciting developments in exoplanet detection, as yesterday’s post about the Near Earths in the AlphaCen Region (NEAR) effort makes clear. Adapting and extending the VISIR instrument at the European Southern Observatory’s Very Large Telescope in Chile, NEAR has seen first light and wrapped up its first observing run of Centauri A and B. What it finds should have interesting ramifications, for its infrared detection capabilities won’t find anything smaller than twice the size of Earth, meaning a habitable zone discovery might rule out a smaller, more Earth-like world, while a null result leaves that possibility open.
The NEAR effort relies on a coronagraph that screens out as much as possible of the light of individual stars while looking for the thermal signature of a planet. An internal coronagraph is one way to block out starlight (the upcoming WFIRST — Wide Field Infrared Survey Telescope — mission will carry a coronagraph within the telescope), but starshade concepts are also in play for the future. Here we separate the space telescope from the large, flat shade making up a separate spacecraft.
Image: Shown here as a potential mission for pairing with the James Webb Space Telescope but likewise applicable to WFIRST, a starshade is a separate spacecraft that blocks out light from the parent star, allowing the exoplanet under scrutiny to be revealed. Credit: University of Colorado/Northrup Grumman.
I’ve been fascinated with starshades ever since learning of the concept through Webster Cash’s work at the University of Colorado Boulder, and discussing with him the possibility of actually imaging distant exoplanets sharply enough to make out weather patterns and continents. But before we get to anything that ambitious, we have to clear the early hurdles, which are numerous. One of them, a big one, is the problem of distance and spacecraft orientation.
Consider: What NASA is looking at right now through its Exoplanet Exploration Program (ExEP) in an effort known as S5 is a pair of spacecraft separated by 20,000 to 40,000 kilometers, using a shade 26 meters in diameter. These numbers aren’t chosen arbitrarily — they mesh with the WFIRST telescope and its 2.4-meter diameter primary mirror, to be launched in the mid-2020s, although a recent report notes that the work is ‘relevant for any roughly 2.4-m space telescope operating at L2.’ As I mentioned above, WFIRST will carry its own coronagraph, but because a starshade is a separate spacecraft, one could join WFIRST in space by the end of the 2020s.
Ashley Baldwin has written extensively about starshades for Centauri Dreams, as a search in the archives will reveal (but start with WFIRST: The Starshade Option). Any consideration of starshades notes the problems to be solved here, as JPL engineer Michael Bottom explains in terms of his work on starshade feasibility for ExEP:
“The distances we’re talking about for the starshade technology are kind of hard to imagine. If the starshade were scaled down to the size of a drink coaster, the telescope would be the size of a pencil eraser and they’d be separated by about 60 miles [100 kilometers]. Now imagine those two objects are free-floating in space. They’re both experiencing these little tugs and nudges from gravity and other forces, and over that distance we’re trying to keep them both precisely aligned to within about 2 millimeters.”
Image: Three views of a starshade. Credit: NASA / Exoplanet Exploration Program.
The S5 team has been working on the technology gaps that have to be closed to allow such a mission to fly given the demands of formation sensing and control. Bottom has come up with a computer program that addresses the issue of spacecraft drifting out of alignment. As discussed in the recent ExoTAC Report on Starshade S5 Milestone #4 Review (‘Milestone #4’ refers to lateral formation sensing and control of the starshade position), a telescope modeled on WFIRST would see the pattern of starlight as it bent around the starshade, a subtle pattern of light and dark that would flag drift down to an inch and less at these distances.
Using algorithms developed by JPL colleague Thibault Flinois, Bottom’s program can sense when the firing of starshade thrusters is needed to return to proper alignment, making this delicate formation flying feasible through automated sensors and thruster controls. It’s also heartening to learn that Bottom and Flinois can demonstrate meeting the alignment demands of larger starshades for future missions, positioned fully 74,000 kilometers from the telescope.
NASA’s starshade technologies became more tightly focused starting in 2016 through a proposal from the ExEP, which anticipated bringing the concept to Technical Readiness Level 5; this is the S5 effort. To put that in context, here is NASA’s overview of what TRL 5 means:
Once the proof-of-concept technology is ready, the technology advances to TRL 4. During TRL 4, multiple component pieces are tested with one another. TRL 5 is a continuation of TRL 4, however, a technology that is at 5 is identified as a breadboard technology and must undergo more rigorous testing than technology that is only at TRL 4. Simulations should be run in environments that are as close to realistic as possible. Once the testing of TRL 5 is complete, a technology may advance to TRL 6. A TRL 6 technology has a fully functional prototype or representational model.
Image: Starshade technology gaps. Credit: NASA / Exoplanet Exploration Program.
There is so much to be analyzed in the starshade concept, from optimal starlight suppression to the stability of the starshade shape and its accuracy in deployment and necessary maneuvering. All of that has to take place within the framework of the above formation sensing and control issues. But Bottom and Flinois’ work has clearly moved the ball. From the report:
Overall, the ExoTAC believes that Milestone #4 has been fully met and congratulates the entire team on their excellent efforts to advance the technology readiness levels of the elements in the S5 activity. Precision lateral control over thousands of kilometers is an unprecedented requirement, and essential for starshade operation. Achieving this first of fifteen S5 Milestones serves as a confidence builder for the entire S5 activity.
We also note that by virtue of the successful achievement of Milestone #4, the Exoplanet Exploration Program’s Technology Gap List item S-3 on “Lateral Formation Sensing” is Retired.
For more on the NASA starshade work, see Starshade Technology Development.
by Paul Gilster | Jun 11, 2019 | Exoplanetary Science |
I marvel that so many of the big questions that have preoccupied me during my life are starting to yield answers. Getting New Horizons to Pluto was certainly part of that process, as a mysterious world began to reveal its secrets. But we’re also moving on the Alpha Centauri question. We have a habitable zone planet around Proxima, and we’re closing on the orbital space around Centauri A and B, a G-class star like our Sun and a cooler K-class orange dwarf in a tight binary orbit, the nearest stars to our own.
At the heart of the research is an instrument called a thermal infrared coronagraph, built in collaboration between the European Southern Observatory and Breakthrough Watch, the privately funded attempt to find and characterize rocky planets around not just Alpha Centauri but other stars within a 20 light year radius of Earth. The coronagraph blocks out most of the stellar light while being optimized to capture the infrared frequencies emitted by an orbiting planet. Note that point: We are talking not about reflected starlight, but infrared emission as a potentially Earth-like planet absorbs energy from its star and emits it at these wavelengths.
The instrument is called NEAR (Near Earths in the AlphaCen Region), developed by teams working at the University of Uppsala (Sweden), the University of Liège (Belgium), the California Institute of Technology and Kampf Telescope Optics in Munich, Germany. Installed at ESO’s Very Large Telescope on one of the four 8-meter instruments there, NEAR upgrades the existing VISIR (VLT Imager and Spectrometer for the InfraRed) to improve contrast and sensitivity, aiming at one part in a million contrast at less than one arcsecond separation.
Remember how daunting a challenge Centauri A and B present. At their most distant, the two stars are about 35 AU apart as they orbit their common barycenter. Orbital eccentricity drops that figure to a mere 11 AU as they close during their 79.9 year orbit. Imagine our night sky if we, like a hypothetical planet around Centauri B, had a G-class star at roughly Saturn’s orbit.
Image: Apparent and true orbits of Alpha Centauri. The A component is held stationary and the relative orbital motion of the B component is shown. The apparent orbit (thin ellipse) is the shape of the orbit as seen by an observer on Earth. The true orbit is the shape of the orbit viewed perpendicular to the plane of the orbital motion. According to the radial velocity vs. time [12] the radial separation of A and B along the line of sight had reached a maximum in 2007 with B being behind A. The orbit is divided here into 80 points, each step refers to a timestep of approx. 0.99888 years or 364.84 days. Credit: Wikimedia Commons.
Then, too, imagine what our view of the universe would be if we had evolved in a place where the night sky held planets around our own star as well as our tight companion, one of which was a habitable world. We have no idea whether such worlds exist around either of the primary Centauri stars, but NEAR has us on pace to learn something soon. My guess is that any civilization in such a setting would have a tremendous spur to develop spaceflight to explore a potential second home that would be within reach of the kind of technologies we have today.
The coronagraph that the NEAR effort brings to VISIR is what should make it possible to detect the signatures of terrestrial-class worlds, just as adaptive optics can screen out atmospheric effects that would distort the vanishingly faint signal (Markus Kasper at the ESO likens this task to detecting a firefly sitting on a lighthouse lamp from several hundred kilometers). NEAR’s ability to reduce noise and switch rapidly between target stars on a 100 millisecond cycle means that in all such operations, precious telescope time is maximized.
Image: ESO’s Very Large Telescope (VLT) has recently received an upgraded addition to its suite of advanced instruments. On 21 May 2019 the newly modified instrument VISIR (VLT Imager and Spectrometer for mid-Infrared) made its first observations since being modified to aid in the search for potentially habitable planets in the Alpha Centauri system, the closest star system to Earth. This image shows NEAR mounted on UT4, with the telescope inclined at low altitude. Credit: ESO/ NEAR Collaboration/.
So where are we now? A ten-day observing run on Alpha Centauri has been conducted since May 23, with observations concluding today. According to the ESO, planets twice the size of Earth or larger should be detectable with the upgraded VISIR. Consider too that working at near- to thermal-infrared wavelengths will allow astronomers to make a call on the temperature of any planet detected with these methods, an obvious clue to potential habitability.
“NEAR is the first and (currently) only project that could directly image a habitable exoplanet. It marks an important milestone. Fingers crossed – we are hoping a large habitable planet is orbiting Alpha Cen A or B,” says Olivier Guyon, lead scientist for Breakthrough Watch.
Data from the NEAR work will be made publicly available from the ESO archive, with a ‘pre-processed and condensed package’ of all the data offered shortly after the campaign ends. This ESO news release notes that a high-contrast imaging data reduction tool called PynPoint has been adapted to process NEAR data. Those without their own data reduction tools can learn more about the software’s installation and setup for NEAR at this PynPoint page.
by Paul Gilster | Jun 10, 2019 | Sail Concepts |
Solar sails are a case of science fiction anticipating the scientific journals, though in an odd way. Engineer Carl Wiley (writing as Russell Saunders) described the physics of solar sailing and some early engineering concepts in the pages of John Campbell’s Astounding back in 1951, but he did it in a nonfiction article of the kind the magazine routinely ran. Richard Garwin would discuss sails in the scientific literature in “Solar Sailing: A Practical Method of Propulsion within the Solar System,” which ran in 1958 in the journal Jet Propulsion.
Then we waited for fictional treatments, which began with Cordwainer Smith’s wonderful “The Lady Who Sailed the Soul” (Galaxy, April 1960) and a string of stories from top authors of the time in just a few quick years — Jack Vance’s “Gateway to Strangeness” (Amazing Stories, 1962), Poul Anderson’s “Sunjammer” (Analog 1964), Arthur C. Clarke’s story of the same name, later renamed “The Wind from the Sun” (Boy’s Life, 1964). Sails of the solar kind had definitely arrived.
Because he is a personal favorite, let me run a clip from the Jack Vance story, which later became known as “Sail 25” (available in various places, but most easily in the 1976 collection The Best of Jack Vance). This is what solar sailing looked like in the days when the nautical metaphor was just beginning to be explored, and a fictional crew is learning, with the help of space veteran Henry Belt, to handle the unusual demands of sail deployment.
“Around the hull swung the gleaming hoop, and now the carrier brought up the sail, a great roll of darkly shining stuff. When unfolded and unrolled, and unfolded many times more it became a tough gleaming film, flimsy as gold leaf. Unfolded to its fullest extent it was a shimmering disk, already rippling and bulging to the light of the sun. The cadets fitted the film to the hoop, stretched it taut as a drum-head, cemented it in place. Now the sail must carefully be held edge on to the sun, or it would quickly move away, under a thrust of about a hundred pounds.
“From the rim braided-iron threads were led to a ring at the back of the parabolic reflector, dwarfing this as the reflector dwarfed the hull, and now the sail was ready to move.
“The carrier brought up a final cargo: water, food, spare parts, a new magazine for the microfilm viewer, mail. Then Henry Belt said, ‘Make sail.'”
It sounded complicated in 1962, but in the era of the IKAROS sail, we’ve learned how tricky actual deployment is, and also how incredibly thin high-performance sails will need to be, particularly as we look toward future missions with cutting-edge materials. Geoff Landis, for example, has examined sails of niobium, beryllium and transparent films of dielectric (non-conducting) materials like silicon carbide, zirconia and diamond-like carbon — a material much like diamond — that could be assembled in space with a plastic substrate.
James Davis Nicoll recently wrote up some examples of sails in science fiction that include the early ones mentioned above, but also more recent work like the novels in Vonda McIntyre’s ‘Starfarers’ sequence and the 1974 tale “The Mountains of Sunset, the Mountains of Dawn.” Also catching Nicoll’s attention is Joan D. Vinge’s “View from a Height,” which should interest anyone exploring the human motivations for immense journeys, and Alastair Reynolds’ Revenger (2016). I hope readers will supply some of their own favorites in science fictional sails. Laser sails play a prominent role in Larry Niven and Jerry Pournelle’s The Mote in God’s Eye (1974), for example, the ‘mote’ being evidence of a sail heading in our direction. And then there’s Forward’s Rocheworld… The list is extensive!
Image: Poul Anderson’s “Sunjammer” appeared in April, 1964, about a month after Arthur C. Clarke’s story of that name, and to make matters even more confusing, ran under the pseudonym ‘Winston P. Sanders.’ Both stories were milestones in early sail depictions.
Like Nicoll, I’m looking back at sail technologies partly because we’re coming up on the launch of The Planetary Society’s LightSail 2, which is now scheduled for no earlier than June 24 aboard a SpaceX Falcon Heavy. The CubeSat spacecraft about the size of a loaf of bread and weighing 5 kilograms will deploy a small sail and attempt to raise its orbit by the momentum imparted by solar photons. I’m a great partisan of CubeSats, particularly those with sail capabilities, for fleets of the inexpensive spacecraft, further miniaturized, networked and tapping solar radiation, can become a great way to deploy sensors all through the inner system.
LightSail is no 5,000-mile behemoth, like the staggering sail of Cordwainer Smith’s story — its four booms will unfurl four triangular panels with a combined area of 32 square meters, and as The Planetary Society’s Jason Davis tells us, the craft will receive a push ‘no stronger than the weight of a paperclip.’ But continual thrust is just the ticket as the effects mount up, and LightSail 2 will be in an orbit high enough (720 kilometers) that the effects of atmospheric drag can be overcome. Expect LightSail 2 to be deployed from the Prox-1 spacecraft that encloses it about seven days after launch. All good wishes on the attempt!
Image: Prox-1 deploys the LightSail 2 spacecraft in Earth orbit. Credit: The Planetary Society (CC BY-NC 3.0).
