by Paul Gilster | Jan 10, 2017 | Exoplanetary Science |
Breakthrough Starshot, the research and engineering effort to lay the groundwork for the launch of nanocraft to Alpha Centauri within a generation, is now investing in an attempt to learn a great deal more about possible planets around these stars. We already know about Proxima b, the highly interesting world orbiting the red dwarf in the system, but we also have a K- and G-class star here, either of which might have planets of its own.
Image: The Alpha Centauri system. The combined light of Centauri A (G-class) and Centauri B (K-class) appears here as a single overwhelmingly bright ‘star.’ Proxima Centauri can be seen circled at bottom right. Credit: European Southern Observatory.
To learn more, Breakthrough Initiatives is working with the European Southern Observatory on modifications to the VISIR instrument (VLT Imager and Spectrometer for mid-Infrared) mounted at ESO’s Very Large Telescope (VLT). Observing in the infrared has advantages for detecting an exoplanet because the contrast between the light of the star and the light of the planet is diminished at these wavelengths, although the star is still millions of times brighter.
To surmount the problem, VISIR will be fitted out for adaptive optics. In addition, Kampf Telescope Optics of Munich will deliver a wavefront sensor and calibration device, while the University of Liège (Belgium) and Uppsala University (Sweden) will jointly develop a coronagraph that will mask the light of the star enough to reveal terrestrial planets.
Image: Paranal at sunset. This panoramic photograph captures the ESO Very Large Telescope (VLT) as twilight comes to Cerro Paranal. The enclosures of the VLT stand out in the picture as the telescopes in them are readied for the night. The VLT is the world’s most powerful advanced optical telescope, consisting of four Unit Telescopes with primary mirrors 8.2 metres in diameter and four movable 1.8-metre Auxiliary Telescopes (ATs), which can be seen in the left corner of the image. Credit: ESO.
According to the agreement signed by Breakthrough Initiatives executive director Pete Worden and European Southern Observatory director general Tim de Zeeuw, Breakthrough Initiatives will pay for a large part of the technology and development costs for the VISIR modifications. Meanwhile, the ESO will provide the necessary telescope time for a search program that will be conducted in 2019. The VISIR work, according to this ESO news release, should provide a proof of concept for the METIS instrument (Mid-infrared E-ELT Imager and Spectrograph), the third instrument on the upcoming European Extremely Large Telescope.
by Paul Gilster | Dec 6, 2016 | Missions |
In early December the Harvard-Smithsonian Center for Astrophysics offered as part of its fall colloquium series a talk by Harvard’s Avi Loeb, fortunately captured on YouTube as Project Starshot: Visiting the Nearest Star Within Our Lifetime. We’ve looked at Breakthrough Starshot in many posts on Centauri Dreams, including my reports from the last set of meetings in Palo Alto, but for those new to the concept of using a laser array to send small, instrumented sails to the Alpha Centauri stars, this video is a fine introduction.
You’ll recall that yesterday I talked about Robert Austin’s futuristic Asteroid Belt Astronomical Telescope, with an illustration of what such an instrument might see of the exoplanet Gliese 832c. If Starshot can achieve its goals, it will be able to make out continent sized features on the surface of Proxima b, or perhaps a planet around Centauri A or B. It would achieve, in other words, what it would take a near-Earth space-based telescope 300 kilometers wide to equal.
Image: What we can see today. The NASA/ESA Hubble Space Telescope has given us this stunning view of the bright Alpha Centauri A (on the left) and Alpha Centauri B (on the right), shining like huge cosmic headlamps in the dark. The image was captured by the Wide-Field and Planetary Camera 2 (WFPC2). WFPC2 was Hubble’s most used instrument for the first 13 years of the space telescope’s life, being replaced in 2009 by Wide-Field Camera 3 (WFC3) during Servicing Mission 4. This portrait of Alpha Centauri was produced by observations carried out at optical and near-infrared wavelengths. Credit: ESA/NASA.
Starshot envisions sending swarms of sails to its target stars, each moving at 20 percent of the speed of light. Each four-meter square lightsail would itself be used as the transmitter dish to beam data back to Earth showing us images of the planet, with each sail sending 100 images over the course of its observations. The time frames are interesting: If all goes without a hitch (and it’s hard to conceive of there being no hitches in a plan this ambitious), it will take several decades to build a beamer and create the actual sails and payload.
Then we have a launch, which takes place in a timeframe of minutes, as a mothership in a highly elliptical orbit releases a sail that is then under the beam for an intense 60,000 g ride. You can imagine all the stresses this puts on the sail, and again, we’ve talked about most of these in previous posts, but Avi Loeb’s presentation offers an excellent refresher, covering factors like sail stability under the beam, sail materials and interstellar dust encounters.
The launch phase ends in minutes and a 20 year cruise phase begins. In the Proxima Centauri system after the journey, each sail now faces an encounter time measured in hours. Thus the pattern: Hurry up and wait. For after the flyby, we face more time, a 4.24 year wait for the first images of the planet to come back to Earth. Interestingly, despite moving at relativistic speed, the planet’s image will remain circular thanks to so-called Terrell rotation.
Loeb mentions as a driver for investigation of Proxima Centauri in particular the fact that M-dwarfs make up a huge percentage of all the stars in the galaxy, and they can live for trillions of years. If we learn that life exists around this kind of star, we learn that living things will have incredibly long timeframes to continue to evolve. We also learn that the kind of environments found around red dwarfs are far more common than what we find around our own familiar G-class star. In many respects, we may wind up being the outliers.
Facets of the Journey
Yesterday I asked what effect being able to see images of planets like Proxima b from telescopes in our own Solar System would have on our thinking. Some would argue that we’ll reach the point where we can learn enough about exoplanets in such observations and will not need to build probes to other stars. My own view is that the two prospects work together. I think any images of a living, Earth-like world around a nearby star are going to focus interest in getting a payload into that system in order to make close up imagery and data possible.
On that score, you’ll recall Project Blue, the attempt to build a small space telescope explicitly designed to detect possible planets in the habitable zones around Centauri A and B (see Project Blue: Imaging Alpha Centauri Planets). Documentary filmmakers who are supporting Project Blue bring Debra Fischer (Yale University), one of its key players, into their new short video Traveling to Alpha Centauri? which explores the same terrain.
Although the video suggests antimatter rather than laser-beamed sails as a solution to the propulsion problem, Fischer’s comments go to the question of what the information we gain from our telescopes can motivate us to do.
If we discover an Earth-like planet orbiting Alpha Centauri, this is really going to drive a whole new era in science, an explosion, to finally go out into the galaxy and to start exploring other worlds.
Fischer goes on to speak of a ‘new wave within humanity to begin taking our steps out of our Solar System’ as a part of achieving the destiny of our species. I’m in agreement, and not just at the level of Project Blue. We could know within a decade or so about possible planets in the habitable zones of the two primary Centauri stars, and we may be able not long afterward to begin analyzing their atmospheres. I believe that hints of life on such worlds will ignite the imagination of the general public in support of projects to explore them up close. To me, Breakthrough Starshot and Project Blue, so different in their scale and conception, are nonetheless two sides of the same coin. An exploring species watches, learns and goes.
by Paul Gilster | Nov 15, 2016 | Exoplanetary Science |
We know about an extremely interesting planet around Proxima Centauri, and there are even plans afoot (Breakthrough Starshot) to get probes into the Alpha Centauri system later in this century. But last April, when Breakthrough Initiatives held a conference at Stanford to talk about this and numerous other matters, the question of what we could see came up. For in Alpha Centauri, we’re dealing with three stars that are closer to us than any other. If there are planets around Centauri A and/or Centauri B, are there ways we could image them?
This gets interesting in the context of Project Blue, a consortium of space organizations looking into exoplanetary imaging technologies. This morning Project Blue drew on the work of some of those present at Stanford, launching a campaign to fund a telescope that could obtain the first image of an Earth-like planet outside our Solar System, perhaps by as early as the end of the decade. The idea here is to ignite a Kickstarter effort aimed at raising $1 million to support needed telescope design studies. A $4 million ‘stretch goal’ would allow testing of the coronagraph, completion of telescope design and the beginning of manufacturing.
Project Blue thinks it can bring this mission home — i.e., launch the telescope and carry out its mission — at a final cost of $50 million (the original ACEsat was a $175 million design). The figure is modest enough when you consider that Kepler, which has transformed our view of exoplanets, cost $600 million, while the James Webb Space Telescope weighs in at $8 billion. About a quarter of the total cost, according to the project, goes into getting the telescope into orbit, which will involve partnering with various providers to lower costs.
But Project Blue also hopes to build a public community around the mission to support design and research activities. Jon Morse is mission executive for the project:
“We’re at an incredible moment in history, where for the first time, we have the technology to actually find another Earth,” said Morse. “Just as exciting — thanks to the power of crowdfunding — we can open this mission to everyone. With the Project Blue consortium, we are bringing together the technical experts who can build and launch this telescope. Now we want to bring along everyone else as well. This is a new kind of space initiative — to achieve cutting-edge science for low cost in just a few years, and it empowers us all to participate in this moment of human discovery.”
I go back to last April because it was at Stanford that I saw Eduardo Bendek’s model of a small space telescope called ACEsat, which was conceived at NASA Ames by Ruslan Belikov and Eduardo Bendek and submitted (unsuccessfully) for NASA Small Explorer funding. Belikov had gone on to present the work at the American Astronomical Society meeting in 2015 (see “How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope,” available here). You’ll recall that Ashley Baldwin wrote up the concept in superb detail on this site in December of that year as ACEsat: Alpha Centauri and Direct Imaging.
Now we have Project Blue, which has connections to the BoldlyGo Institute, its offshoot Mission Centaur, the SETI Institute and the University of Massachusetts Lowell. The aim is to launch a space telescope with a 45-50 centimeter aperture, looking for potentially habitable planets from 0.5 to 1.5 AU within the habitable zones of both Centauri A and B. The ultimate hope, then, is to ‘see blue’ — meaning oceans and atmosphere, a world on which life could emerge. This is Sagan’s ‘pale blue dot,’ only now it’s not our own planet but an Earth 2.0.
The Project Blue space telescope would spend two years in low Earth orbit accumulating image after image — hundreds, thousands, tens of thousands — as a way of teasing out its faint targets. When it comes to ‘another Earth,’ Centauri A and B up the ante on Proxima Centauri. The Proxima planet may well be habitable, but a true Earth analog is not going to be tidally locked to its star, as Proxima b probably is, and it’s not going to orbit a red dwarf.
Neither Belikov or deputy principal investigator Eduardo Bendek are formally connected to Project Blue, but their work in the form of papers and conference presentations feeds directly into the concept driving the project. The original mission now cedes the floor to the private sector, whose job it will be to raise enough cash to support the development of the needed coronagraph to filter out the light of two very close stars, along with other key flight hardware elements. The next step, though, long before building flight hardware, is to finalize the telescope design.
The new Kickstarter campaign will pay for analysis, design, and simulations, but Project Blue has an eye on other partnerships as well as wealthy donors and foundations. Usefully, the project should be able to test coronagraph technologies similar to those being considered on much larger space instruments currently under study by the major space agencies, thus providing a useful testbed for such designs. To make this work, everything must fall into place — the coronagraph for starlight suppression, a deformable mirror to feed the coronagraph and rock-solid stability. No aspect can be allowed to fail if the mission is to achieve its goal.
If the Project Blue planners are correct, we can solve the attendant problems and get this mission into space is as little as 4 to 6 years. The goal is hugely ambitious but it also opens the door to citizen-science, with private donors contributing to an instrument that will not be the result of a government program or a for-profit commercial space effort. The initial Kickstarter campaign is designed to bolster the technical groundwork needed for the telescope, but stretch goals could see publicly funded flight component manufacturing.
Looking for Earth-like planets around other stars is like looking for bioluminescent algae next to a lighthouse. But I keep coming back to that Breakthrough Discuss meeting in Stanford, because I remember Ruslan Belikov telling his audience that the key advantage of Alpha Centauri is how large the habitable zones around its component stars appear in terms of angular size. We would need a significantly larger instrument to attempt something similar around other nearby stars. The Alpha Centauri stars are nature’s gift, and it’s one we would do well to exploit. Check the Kickstarter page for more on this low cost, high impact idea.
For more on the technical background of the ACEsat concept, see Belikov et al., “How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope” (preprint) and Bendek et al., “Space telescope design to directly image the habitable zone of Alpha Centauri” (preprint).
by Paul Gilster | Apr 20, 2016 | Astrobiology and SETI |
Heading for the hotel lobby the first night of the Breakthrough Discuss meeting, I thought about a major theme of the Breakthrough Starshot initiative: Making things smaller. Robert Forward wrote about sails hundreds of kilometers in diameter, and vast lenses deep in the Solar System to collimate a laser beam that would drive them. But Breakthrough Starshot is looking at a sail four meters across, carrying a payload more like a smartphone than a cargo ship. That big lens in the outer system? No longer needed if we can power up the sail close to home.
How to Look at Alpha Centauri
Digitization works wonders, and Moore’s Law takes us into ever smaller and more tightly packed realms on silicon chips. The trend affects every aspect of spaceflight and astronomy, as witness ACEsat, a small coronagraph mission with an explicit mission, the search for planets around Alpha Centauri A and B. Ruslan Belikov (NASA Ames), working with Northrop Grumman, led the team that conceived this mission, which was recently submitted for NASA Small Explorer funding. The funding did not come through, but the ACEsat idea persists.
At Breakthrough Discuss, we heard Ruslan Belikov describe the mission. Lead author of a recent paper on the work (“How to directly image a habitable planet around Alpha Centauri with a 30-45cm telescope,” available here), Belikov showed a half-scale model of ACEsat that was small enough to hold in your hand. The mission as currently conceived uses a 35 centimeter by 18 cm optical mirror, fits into a CubeSat, and in the view of its creators, is capable of directly imaging Earth-like planets around Alpha Centauri (see ACEsat: Alpha Centauri and Direct Imaging, Ashley Baldwin’s article from last December, for more).
“Alpha Centauri isn’t the tip of the iceberg,” Belikov told conference attendees during a panel discussion on exoplanet detection. “It is the iceberg. We know that small stars like Barnard’s Star or Proxima Centauri have small habitable zones. But nature has given us Alpha Centauri, a favorable outlier — think about how large its habitable zone appears on the sky in terms of its angular size. We would need a telescope three times larger for other stars.”
Image: Stars in the Alpha Centauri system as compared with the Sun. Credit: David Benbennick. CC BY-SA 3.0.
When asked what surprises we would find around the Alpha Centauri stars, Sara Seager (MIT) suggested that the biggest surprise would be finding a true Earth twin with life on it, and Belikov was quick to agree — “Sara stole my answer,” he said with a laugh. But Seager would go on to talk about future telescopic efforts focusing on just one object, one specialized type of telescope for each type of star. That more specialized approach seems to fit in nicely with Belikov’s ACEsat concept, tuned as it is for not just a specific type of star but a specific stellar system.
Cornell’s Lisa Kaltenegger urged the audience to think about an Earth ‘twin’ being utterly unlike what we might imagine:
“A world like this could meet our conditions for habitability and yet be much different from the Earth. We can imagine a different kind of biota taking over. When you think about an Earth twin, don’t think about the picture you know. Think yellow, think green, whatever color you want. We can look at some of the exotic deep water fish we find in the ocean and realize that they, as strange as they seem, evolved right here. What might wind up evolving around Centauri?”
Kaltenegger’s remarks drew on her work at the Carl Sagan Institute, where she has built a new interdisciplinary research group spanning ten departments. The effort includes a color catalog that examines the differing reflectivity of various planets depending on possible biota. Which gets us to a major point about Breakthrough Starshot. As Kaltenegger mentioned more than once, data return from the nearest stars needs to include more than basic photographic images. Spectroscopic analysis is crucial as we examine planetary atmospheres for biosignatures.
Natalie Batalha (NASA Ames) pointed out that while we all hoped to find planets in the habitable zone of Alpha Centauri, we might consider that a null result there could still leave us with interesting science. We have not resolved the surface features of any main sequence star except for our own Sun. An Alpha Centauri mission gives us the prospect of resolving the surface of three stars, a science windfall that adds to the benefits of the mission.
Image: Exoplanet hunters Sara Seager (left), Lisa Kaltenegger, Natalie Batalha and Debra Fischer during a break at the meeting.
SETI and Its Consequences
The question and answer sessions at Breakthrough Discuss tended to run into our break periods, when many of the issues continued to circulate. A key issue for SETI is that factor in the Drake equation that addresses the lifetime of a technological civilization. Just how long do such entities survive? It’s an issue that lies like morning fog over the SETI landscape as we look at our own problems with the proliferation of powerful weapons systems and ask what happens when small organizations, even individuals, can acquire ever more deadly capabilities.
Here Harvard’s Avi Loeb brought up a point many others had been thinking about, to judge from the ensuing conversations outside. We naturally focus on finding biological life because that is what we are, but the technologies we are discussing remind us off the possibility that life transforms at a certain level of its development into a technological phase that leads to post-biological intelligence. Sara Seager pointed to existing tools like pacemakers and artificial limbs — if life goes post-biological, how do we create a SETI capable of identifying it?
For that matter, what do we do if it’s non-biological, as Denise Herzing (Florida Atlantic University) asked. Researching dolphin communication through the Wild Dolphin Project, Herzing wonders what the signatures of a non-technological species might be. We are only beginning to understand the complexity of dolphin communication. What if a Breakthrough Starshot mission encounters a world with an intelligent, non-technologial species in charge? Is there any way we could identify it?
The SETI session itself, led by Jill Tarter, focused on optical SETI and the new directions it opens to scrutiny. Again, the issue seems timely given the nature of the Starshot initiative, for as we conceive of technologies here on Earth, we then must ask whether equivalent technologies would be visible to us. Breakthrough Starshot envisions using phased laser arrays scaling up to the 100 GW level. As we learn how to create such ‘beamers,’ we have to ask whether the most common SETI signature in the optical might not be transient pulses that are the byproducts of other activities rather than intentional efforts to communicate with us.
Image: Jill Tarter takes the podium to begin the SETI session.
Puzzlingly, Jim Benford’s paper on that very idea was put into the session on using the Sun as a gravitational lens, but the methods Benford is discussing are very much part of the optical SETI landscape. Centauri Dreams readers already know Benford’s findings: Depending on the use of the beamed energy technology, we would indeed be able to detect transient signals from another star with equipment existing today (see Quantifying KIC 8462852 Power Beaming for background). See also “Power Beaming Leakage Radiation as a SETI Observable,” available here).
Moreover, there does exist a communications dimension, as Benford explained:
“SETI messages may be found on power beaming leakage. That leakage is more powerful than any beacons we’ll ever be likely to build, so we should look at transient signals to see if there is a message embedded on them.”
Beamed energy options for an advanced civilization might involve everything from microwave thermal rockets (beaming to orbit) to orbit boosting to interplanetary and even interstellar missions. With each of these missions, you get progressively higher energy usage. And we can certainly go beyond this list of applications into areas like asteroid deflection, which might one day be necessary to adjust a dangerous trajectory using a high-powered laser. Another possibility: Using a beamer to create a thrust (by evaporation and desorption) of a comet’s surface, which might be a technique one day used in terraforming a planet like Mars.
Benford points out that given their visibility over interstellar distances, many of these uses of beamed energy should make us reconsider optical SETI strategy. Rather than focusing on narrow-band transmissions of the kind likely to be found in a beacon, we should look for more powerful beams with a wider bandwidth. Whereas earlier optical SETI work has involved the 1 ? 10GHz microwave band, we might, considering our atmosphere, want to examine bands where lower oxygen and water vapor allow transmission, which means windows at 35GHz, 70 ? 115GHz, 130 ? 170GHz and 200 ? 320GHz.
The caveat is that power beaming is not isotropic but highly directed. The geometry is not always going to favor detection — the fact that we do not see the beam does not mean that it is not there. An interesting suggestion is to revisit the thousands of transients that have been observed and are now stored in the archives of the SETI@home project.
James Guillochon (Harvard) examined rapid travel in the Solar System via lightsails powered by beamed radiation, underlining some of Benford’s points. A lightsail network in the Solar System is the kind of SETI observable Benford and son Dominic have already addressed in their upcoming paper, the point being that leakage around the edges of the sail cannot be avoided. You may recall that Guillochon, working with Avi Loeb, discussed SETI possibilities in 2015 in “SETI via Leakage from Light Sails in Exoplanetary Systems,” available here).
Image: Beautiful weather and a Palo Alto spring made the occasional break a welcome chance to relax.
But enough for today. More SETI discussion tomorrow, after which we move into the Breakthrough Starshot mission itself as described by former NASA Ames director Pete Worden, and the possibilities of the Sun’s gravitational lens as both a mission target and a mission facilitator.
by Paul Gilster | Apr 19, 2016 | Exoplanetary Science |
At Palo Alto’s superb Amber India, I was thinking about Alpha Centauri. There are several Amber India locations in the Bay area, but the Palo Alto restaurant dishes up, among other delights, a spicy scallop appetizer that is searingly hot and brilliantly spiced. Greg and Jim Benford were at the table, Claudio Maccone and my son Miles. It was the night before Breakthrough Discuss convened. And while the topics roamed over many aspects of spaceflight, it was that star system right here in our solar neighborhood that preoccupied me.
How lucky could we be to have not one but two stars this close and so similar to our own? Centauri A is a G-class star, Centauri B a K, and if we hit the jackpot, we could conceivably find planets orbiting both. Then there is Proxima Centauri, an M-dwarf that is the closest star of all to the Solar System. The presence of so many astronomers on the Breakthrough Discuss roster made it clear we’d get the latest on the hunt for planets here, a vital factor as we assessed prospects for the Breakthrough Starshot mission. A nice blue target world would help.
The Binary Star Factor
Growing up, I would haunt the local library for books on astronomy, learning that despite its tantalizing proximity, Alpha Centauri was likely devoid of planets because Centauri A and B were so close to each other. After all, at times they close to within 11 AU — how could planets exist in such a gravitationally unsettled region? The question is still unanswered, as is the question of whether Proxima Centauri is truly part of a triple star system or simply shares a common motion with A and B. But our picture of Alpha Centauri has changed radically since my days in the local library, and the system is under scrutiny as never before.
Image: Gathering outside Stanford’s Arrillaga Alumni Center with coffee in hand as we waited for the first session of Breakthrough Discuss to begin.
Paul Wiegert and Matt Holman discussed stable orbits around Centauri A and B back in 1997, work that led to a generally accepted belief that out to a distance of perhaps 2.5 AU, small planets of Earth-like radius or a bit larger could exist. Giant planets are seemingly ruled out by radial velocity studies, although Jared Males (University of Arizona) would note that we might save James Cameron’s Polyphemus, a gas giant in the film Avatar, by postulating a large radius, low mass planet. But he was quick to add that the prospect was not likely.
The session, titled Exoplanet Detection Programs Focused on Alpha Centauri, was led by Olivier Guyon, but it was Michael Endl (University of Texas at Austin) who presented the overview of Alpha Centauri work so far. The issue of planet formation is far from settled, and as Centauri Dreams readers know, the question is not so much one of stable orbits but whether planet formation can deliver an intact planet in the first place. Key work here has been done by Philippe Thébault and Javiera Guedes, who have reached opposite conclusions, with Guedes arguing for small planet formation, and Thebault arguing against the proposition because of planetesimal encounters and the impact velocities at which they would occur.
Image: One of Michael Endl’s slides, this one discussing planet formation around Alpha Centauri.
The argument will be settled, as Endl pointed out, by our increasingly powerful ability to deploy new technologies. Radial velocity methods are pushing toward the region we’ll need to study, but even now we would need to work at a 10-12 centimeters per second level to find an Earth mass planet, a feat that Endl noted was orders of magnitude below what today’s best instruments can deliver. Remember, too, that the planet we thought we had found around Centauri B probably isn’t there, now considered to be a false positive probably caused by activity on the star itself. In fact, let me quote Xavier Dumusque on this, as he was at the conference and was on the team that performed the original Centauri B work:
We worked with 20,000 spectra on Centauri B taken over four years and found a small 50 cm per second signal that seemed to be a planet in a 3.2 day orbit. Subsequent papers have shown that the signal is in the data, but it is probably not due to a planet. All our techniques are at the limit of their capabilities, which means we should use all the techniques we have, so that if one tells us we have a planet, another can assure us it is real.
The problems Alpha Centauri presents, particularly right now, are manifest. Spectral contamination means that when you’re trying to tease a Doppler signal out of the light from a star like Centauri B, you get light mixing in from Centauri A, for at this point in their orbits, the two stars have closed to their closest point as viewed from Earth. The work Dumusque referred to, drawn from HARPS spectroscopic data at the European Southern Observatory’s La Silla Observatory, may well have been affected by magnetic effects on Centauri B’s surface. But right now we’re in that period when the primary Centauri stars are very hard to analyze.
I’ll remind readers that there has been one possible transit detected. Motivated by the HARPS work on the possible 3.2-day period planet, the search turned up what looked like the transit of an Earth-like planet with a period of less than 12 days, but if it was a transit, it did not recur. As to Proxima Centauri, we still have no planets there, but we can rule out larger worlds, while allowing the possibility of planets of two to three Earth masses in the habitable zone. We’ve followed the work of the Pale Red Dot project that has collected new spectra using the HARPS instrument in these pages and are awaiting the data analysis with great interest.
Image: Natalie Batalha (NASA Ames) raising a point during the panel discussion that followed the Alpha Centauri planet detection talks.
Bringing New Methods to Bear
The point that Michael Endl made, and it was echoed by other speakers, is that we need to throw everything we have at this intractable problem. One way forward is to keep improving radial velocity precision, but we also need to do x-ray monitoring of Centauri A and B to look for activity cycles, and consider the possibilities of astrometry and even direct imaging. Thomas Ayres (University of Colorado) noted the dramatic changes to Alpha Centauri A in x-ray imaging — the star goes dark at x-ray wavelengths in 2005 with an unprecedented darkening by a factor of 50, and is now showing a return to activity levels close to that of our own Sun.
The scientists at Breakthrough Discuss were generally upbeat about the prospects of finding planets in the Alpha Centauri system, though the feeling was not quite unanimous, with Peter Tuthill (University of Sydney) saying he found the likelihood of planets there in the range of 20 percent. Adding “I’ve just put myself out of a job with that comment,” he went on to explain JAM, the JWST Aperture Mask, which would use astrometric methods to look for the tiny stellar motion that a planet tugging either Centauri A or B would induce. A separate mission called TOLIMAN (a medieval name for Alpha Centauri) would use a diffractive pupil aperture mask, with the distortions optical systems produce becoming a ‘ruler’ that detects such motion.
Image: A view across the way from the alumni center during a break. After the intense sessions, it was a pleasure to walk outside for a few minutes to rest my eyes.
And what about observing Alpha Centauri planets from the ground? We’re moving into the era of enormous ground observatories with apertures from 20 meters up to 100 meters across in the works. These Extremely Large Telescopes (ELTs), like the European Extremely Large Telescope (Chile), the Thirty Meter Telescope (Mauna Kea, Hawaii) and the Giant Magellan Telescope (Chile) point toward future instruments as enormous as Colossus, a 100 meter telescope concept that could become the world’s largest optical and infrared instrument.
Needless to say, such instruments can become major tools for studying planetary systems around nearby stars. But as Markus Kasper (European Southern Observatory) explained, we can also perform upgrades on existing instruments — the Very Large Telescope (VLT), Magellan (Chile) and Gemini (sites in Hawaii and Chile) — to perform pathfinder work at thermal infrared wavelengths for future imaging with the giant instruments to come. Thus ground-based instruments become a complement to space telescopes for actual exoplanet imaging.
I was interested in Bruce Macintosh’s presentation on direct imaging from space, because years ago I talked to Webster Cash (University of Colorado) about the prospects of using a starshade, in which the optics for a mission are separated. Rather than using a coronagraph to block out the light of the central star, you create a starshade whose shape is precisely determined to block the same light, with the starshade operating some 25000 kilometers away from the telescope.
Macintosh (Stanford University) said the problem of seeing a planet next to the blazing star that it circles was akin to looking for bioluminescent algae next to a lighthouse, which is why we need a coronagraph or a starshade in the first place. The WFIRST mission (Wide-Field Infrared Survey Telescope), scheduled for launch late in the next decade, will carry an advanced coronagraph, but a starshade would also be compatible with this instrument.
Image: The starshade in position far from the space telescope observing the light, with the central star effectively masked. Credit: University of Colorado.
But maybe we don’t have to wait that long. During a break I had the chance to talk to Cash, who had been a huge help with my original Centauri Dreams book. Cash has been working with starshade concepts for a long time, but even he was surprised when his team began testing small starshades in the atmosphere. In a field of view that included the bright star Sirius, the star would simply disappear. While continuing work on a space telescope/starshade concept called the Aragoscope (after French optical scientist Francois Arago), Cash and team began testing an airborne starshade that could be observed by a telescope on the ground.
All of this could lead to serious results at Alpha Centauri. Cash hopes to use an airborne starshade no more than a meter across that will be observed by a balloon-lofted telescope several hundred kilometers away to probe the habitable zone of Alpha Centauri. “Anything you can do on ground, you should do on ground,” Cash explained. “If we can do it remotely with big telescopes, it’s not a key part of payload that actually goes to Alpha Centauri.”
I’m running out of time today, so I’ll start tomorrow with an Alpha Centauri observing platform called ACEsat, a dedicated space observatory, and move from there into some of the more speculative thoughts of the attendees on what we might find around these stars.
