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First Light for NEAR: Searching for Planets around Centauri A and B

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.

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{ 30 comments… add one }
  • Harry R Ray June 11, 2019, 9:43

    Paul Gilster: Do you know what the distance-from-star minima and maxima for potentially observable planets are for each star. If a planet is too close to a star, it would be within the coronograph and be unable to be imaged. If a planet is too far away, it would be too cold to be observed. I also assume that planet radius minima would be 2Rearth at the distance from star minima and increase with distance until it reaches the distance from star maxima.

    • Paul Gilster June 11, 2019, 10:56

      I don’t have this information, I’m afraid.

  • Brett June 11, 2019, 10:58

    According to the ESO, planets twice the size of Earth or larger should be detectable with the upgraded VISIR.

    I don’t think it’s going to find any habitable exo-planets with that limit. The modeling and prior exo-planet research overwhelmingly suggests that planets with radii 2 times Earth or larger are gas dwarfs or water-mantle worlds, nothing Earth-like.

    Imagine our night sky if we, like a hypothetical planet around Centauri B, had a G-class star at roughly Saturn’s orbit.

    It’d be quite the view. If you were on such a world orbiting Centauri A, you’d see Centauri B gradually move further and further away from A in the sky across the course of the year, until the planet was between them. At which point “night” as we know it disappears for a while because there’s always one or the other lighting its surface, and then B starts getting closer and closer to A in the sky.

    • Alex Tolley June 11, 2019, 14:44

      A short period version of Lagash from Asimov’s Nightfall, but in reverse. The planet experiences a loss of night, rather than day.

    • andy June 11, 2019, 14:59

      I don’t think it’s going to find any habitable exo-planets with that limit. The modeling and prior exo-planet research overwhelmingly suggests that planets with radii 2 times Earth or larger are gas dwarfs or water-mantle worlds, nothing Earth-like.

      Yeah, I don’t think you get to claim a planet of 2 Earth radii (or more) is terrestrial these days unless you have a mass measurement. Of course, the current planet sample is biased towards shorter periods, so maybe the processes that build planets at ~1 AU or so end up producing rockier worlds than systems that migrate planets in to orbits of a few days or so. Plus the discs of Alpha Centauri AB should have been truncated somewhere near the snowline, so maybe drier worlds are more likely…

  • Spaceman June 11, 2019, 12:53

    Any word as to when the upgraded instrument will start making observations?

    • Paul Gilster June 11, 2019, 13:54

      The first 10-day observation run ends today, with results soon to be released.

  • andy June 11, 2019, 14:47

    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.

    I’d imagine that having a second star in the sky would make stellar/galactic astronomy more difficult, what with the contamination of the sky. Imagine having to run a Gaia-/Hipparcos-like mission for 80 years to get a good view of the complete sky!

  • john walker June 11, 2019, 14:56

    Hope something shows up. At the stated 1 arcsecond resolution, HZ planets around Alpha A might be detectable. It’s right at the limit. Not around B. That would require resolution of at least 0.5 arcseconds.

    Breakthrough Watch had earlier plans to launch
    a 30 cm instrument into orbit in order to attempt planet detection through astrometric means. By monitoring the angular separation of the binary down to 2 microarcseconds. No idea if this is still an active project.

    It’s worth mentioning that planetary formation models for this binary have become more restrictive over the years. Today many simulations rely on an assumtion of greater initial separation of the two primaries during the accretion phase in order for terrestrial planets to form. Would be a shame if these two stars which separately each seem well suited for the formation of habitable terrestrial planets were destined to exist so close to each that they rob each other of that chance. Hope that’s not the case.

  • Bruce D. Mayfield June 11, 2019, 15:10

    “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.

    We can’t blame them for hoping to find to find such a large planet(s) with their new equipment, but it would give much more impetus to interstellar mission development if what is found in one(or two) of these Alpha Cen HZs is(are) planet(s) close to Earth’s radius. Therefore a non-detection from NEAR at this point wouldn’t be bad news.

    • Harry R Ray June 11, 2019, 17:03

      NEAR is NOT the (currently)only project that could directly image a habitable exoplanet. It is the only ACTIVE one. Last year I reported that a high amplitude pupil mask has been ASSEMBLED AND TESTED that could be installed on the OPTICAL “ZIMPOL” instrument, allowing it, when combined with SPHERE, to have a reasonable chance to image Proxima b! So far, I have heard of no proposal being accepted to do this anywhere in the near future, and perhaps of even one being MADE. I assume that the main reason for this, is that an OPTICAL image of Proxima B would yield relatively LITTLE scientific information about the planet(i.e. NO spectra, NO radius, because reflected optical light is albedo dependent, and NO temperature). ESO hopes to obtain this information PRIOR to JWST doing so with their SPHERE/ESPRESSO package, which would be done WITHOUT an ACTUAL “image”, but instead only through phase curves, and would take three years to complete. If both NEAR and SPHERE/ESPRESSO are successful, there may NEVER be an attempt to image Proxima b in the optical, despite the great HISTORICAL value of such an image.

      • Bruce D. Mayfield June 11, 2019, 19:58

        Never? Proxima b would be an important, historic target for any future observatory and team to bag by direct imaging. True, what can be learned from DI might be very little, but the confirmation value might be great. Such an image might be needed to help garner enough support to mount a mission to Proxima. Remember the old adage, “Seeing is believing.”

  • Ashley Baldwin) June 11, 2019, 16:18

    NEAR was originally intended to have a twenty day observation run as part of Breakthrough , “chopping” between the two constituents of the AB binary. This to capture a significant “pixel” based fraction of an erstwhile planet orbiting at 1AU from either star.( sat just within the hab zones of both) .

    NEAR itself is intended to act as a prototype of the METIS NIR spectrographic imager slated for the E-ELT. It would operate in the “N band”, with a bandwidth set between ten and twelve microns. This was selected as near the longest wavelength practically imaged from the ground ( allowing for telluric and systematic background emissions ) but to cover the thermal emission of a terrestrial style exoplanet atmosphere . It also covers any exoplanet ozone emission peak. At this much longer than optic wavelength the contrast difference between stars and planets drops to as low as 1e7 – within the capabilities of a high performance coronagraph combined with image post processing. ( as opposed to the much more demanding nee impossible 1e10 at optical) .

    The VISIR NIR imager on the Unit telescope 3, UT3, of the VLT array has recently had just such a ( vector vortex) coronagraph installed . To create the NEAR instrument, VISIR has been temporarily moved to UT4 – along with its supercooling equipment . UT4 has also recently been upgraded , in this instance with a deformable secondary mirror . Effectively creating the high performance adaptive optics, AO, necesary to remove wavefront and instrumentation errors to allow direct imaging of terrestrial style exoplanets require if combined with VISIR. High performance AO have stringent construction requirements and NEAR represents the first time a high performance imaging instrument like VISIR has been combined with them . The 8.2m UT4,though large, still lacks the resolution to image potentially habitable planets – except around Alpha Centauri – so poses a unique cost effective opportunity to pilot METIS technology.

    In terms of its sensitivity it can potentially image a 1.9 Re Earth with an Earth like atmosphere emitting at Earth like temperatures . However this drops to 1.3Re if emitting at a temperature of 325 K. With a spectrum of variations inbetween.

    I’m not sure if I want Breakthrough to succeed. Yes and no I guess. Yes, it would be great to finally find planets around Alpha Centauri – especially if terrestrial and in a habzone. No, because if anything is found it is likely to be a mini Neptune at worst , sitting just where we don’t want it – slap bang in the hab zone . At best ? A Super Venus perhaps .

    Maybe a “Dune” style desert planet. But that’s probably just me being fanciful. But to end on a positive note , if NEAR finds anything then it’s all systems go for METIS. On a telescope five times wider.

    • Harry R Ray June 11, 2019, 17:35

      To me, a 3 Earth radius “water world” with Earth-like temperatures would be a MAJOR SUCCESS! A recent paper stated that 3 Earth radius planets were MORE LIKELY to be water rich with a relatively thin(i.e in the range of Earth to Venus, so that the star would be visible in a cloudless sky) than be a rocky core with a crushing hydrogen atmosphere. This premise is yet to be PROVEN, so it would be of GREAT IMPORTANCE if we could actually find one! If we do, even though such a planet is probably not able to produce life as we know it on its own, it could still have life transported to it via panspermia, either via a yet to be imageable Earth-sized planet in the HZ of the other star, or via a moon slightly more massive than Mars orbiting IT!

    • ljk June 12, 2019, 9:08

      Or how about an Earth-like exomoon orbiting a gas giant world…

      https://en.wikipedia.org/wiki/Fictional_universe_of_Avatar

      • Harry R Ray June 13, 2019, 9:40

        Pandora fan, I see. Unfortunately, Fisher and Laughlin’s long-running Alpha Centauri A and B radial velocity observations taken by the Terra Sololo observatory(confirmed by a rival group using the Mc Donalds observatory)have unequivically ruled out any habitable zone planets of 1/2 Saturn mass or more around both stars. However, there still renains a sliver of hope. A recent paper.states that the habitable zone outer limit for exomoons could be moved much further outward if the parent planet induces even mild tidal friction in one exomoon due to perterbations of other exomoons, like what is happening with Jupiter’s Europa and the affected exomoon also has sufficient CO2 in its atmosphere to take advantage of the residual heat produced by such tidal friction.

        • ljk June 18, 2019, 10:05

          If that world has enough unobtanium at 10 million dollars a gram, I guarantee we will have our first interstellar expeditions in no time.

  • Robin Datta June 11, 2019, 17:54

    If the many widely varying telescopes around the world could be approached as ommatidia, individual units in a compound arthropod eye, the crying need would be for an infrastructure to tie them all together into one instrument with an objective diameter for image resolution approaching that of our Blue Planet. With the ubiquity of mobile devices, it might not be too far-fetched an idea. It could even be looked upon as an extension of SETI@home.

    • Ron S. June 11, 2019, 22:33

      Optical interferometry is very, very difficult. It requires exquisitely precise phase matching of signals at a frequency of hundreds of THz. The technology to do this electronically (as is done for radio VLBI up to the GHz range) is far off. For now optical interferometry must be done with optical phasing harnesses cut and aligned to precisely identical optical lengths, where precise is to within ~1000 Angstroms for visible light. And there are other challenges. I won’t attempt to say more since I have no expertise in this field.

  • Laintal June 11, 2019, 22:03

    Hi

    A very interesting article Paul and I liked your intro “marvel that so many of the big questions that have preoccupied me during my life are starting to yield answer” Me too as well.

    Its a shame an Earth Sized world or smaller would be missed but I’m sure searches and equipment are only going to improve with time.

    Thanks Laintal

  • Ashley Baldwin) June 12, 2019, 3:56

    What you are talking about is essentially an optical interferometer with its “synthesised aperture”. As originally envisage by Michaelaon and widely used in radio telescope/sub millimetre arrays like ALMA.

    The most high profile example being the recent creation of the Event Horizon telescope linking radio telescope arrays worldwide to give the incredible resolution required to image the M87 supermassive balance hole. In theory linking optical telescopes in a similar manner could create an interferometer to actually resolve images of nearby exoplanets let alone see them and expose them to detailed spectroscopy. Suitable combination of their individuali inputs could even also create an interferometric coronagraph in theory too . Unfortunately and without going into detail, the principle of aperture synthesis for the much shorter and energetic optical wavelengths ( nanometres versus millimetres) requires inaccessible levels of processing power ( Event Horizon stretched currently available computational power ) to combine the multiple individual telescope inputs into an “equivalent” high energy electrical field before converting this to an individual image.

    Even then any exoplanet is going to be incredibly dim in relation to say the M87 black hole ( or it’s attendant accretion disk anyhow) with even multiple telescopes still not collecting enough photons to work with. There are small optical interferometers available , like CHARA, whose small size and uncomplicated design allows targeting of bright targets ( stars – with a magnitude of no less than 8- versus an exoplanet with a magnitude of 22 ) but these are still expensive to design and construct and being small can utilise currently available computation.

    That said it might be at some time in the future that optical/infrared interferometry does become viable on Earth or in space ( NASA’s SIM and ESA’s Darwin were just such concepts) and will drive a new era in exoplanet science.

  • Laintal June 12, 2019, 6:11

    People might enjoy this one

    Frequency of planets orbiting M dwarfs in the Solar neighbourhood
    https://arxiv.org/abs/1906.04644

    • Michael Fidler June 12, 2019, 8:43

      341 pages!

  • Spaceman June 12, 2019, 10:43

    Assuming that either Alpha Centauri A or B has a compact planetary system with several mini-Neptunes and/or super-Earths all, say, within 0.3 A.U, will the NEAR observations be capable of detecting this type of configuration? Or, is NEAR optimized for detections of planets specifically only at or near 1 A. U. ?

  • wdk June 12, 2019, 16:26

    Back in the 1980s and 90s, spent some time playing with the problem of
    planets in orbit around Alpha Centauri A or B, along with some of the other well known binary systems nearby ( Sirius, Procyon, and others).
    It was tantalizing because Alpha Cen was close by and would be such an interesting place for an Earth like planet to live ( dual sun rises and sun sets or other holidays). And then (bonus!) if you really wanted to go somewhere interstellar, there was always the possibility of visiting cousins orbiting the other sun.

    The dynamics of planetary motion were intriguing too. Would a planet work?

    Back then the science fiction and science communities didn’t talk to each other very much about this question. So, doing conventional orbital analyses ( finite burns of rockets in orbit, etc.), I cut and pasted some FORTRAN programs into something that could handle
    “stellar-centric” situations where there were two suns and one insignificant planet. It was generalized to handle the highly eccentric
    cases involved ( ~0.5), unlike the solar system cases that a lot of
    dynamic research focused on. Here and there, of course, I read of other
    people examining this, but wanted to try it out anyway. Technically this would be a distinct member of the restricted three body problem, the restricted ELLIPTIC three body problem.

    Might have mentioned before the technique of taking the sun’s surface temperature and estimating what the temperature would be if it went out to the Earth’s orbit. About 400 degrees Kelvin vs. about 5800.
    Used this as a criterion for searching for other Earths with tolerances
    of maybe 50 degree increments hotter or colder.

    So given that assumption, certain things fell out for analogs to Earth around Alpha Centauri A and B as indicated in the table below compressed from paper results.
    ===========================================
    Teff (Ro) Nominal 2-Body Eccentricity Cycle
    Star Temperature Rad Ro Period Period Mag Osc
    Component (oK) ( AUs) (days) (Kyrs) (DeltaR/Ro)
    ____________________________________________
    Alpha 400 1.2468 484 8.0 0.08, -0.09
    Centauri 350 1.6285 724 5.0 0.11, -0.12
    A 300 2.2165 1,149 2.6 0.12, -0.15
    Alpha
    Centauri B 400 0.6438 204 15.8 0.05, -0.05
    =========================================
    These values might give some perspective on the separations.
    The system is 1.3 parsecs away. Planets with earth-like conditions
    might be separated by nearly the same baseline as we use for the
    parallax measurements. At best they could separate about an arc second
    from the primaries? (e.g. the Star shifts due to parallax, but the planet
    appears to be in the straight line position).

    There were data for a lot of other star systems too. And doing this
    was not as boring, say, as taking pi out to the nth decimal. But it
    was clear that things orbiting in binary systems like this would gyrate
    in ways that we were not accustomed to in the Solar System, save
    for asteroids and comets.

    And for cases like Sirius A and B, there were no stable orbits for earth like planets. So if you are expecting V coming from there, forget about it, I couldn’t keep a circularized planet circular at all and they got
    thrown out in a few thousand years, if not burned up.

    The other Dog Star was a little more borderline.

    But I make these distinctions looking over my shoulder. Alpha Centauri B is a more stable site than A and Alpha Centauri A is more stable than Procyon A, but are they sufficiently stable for terrestrial planets to last?
    Or form in the first place? That’s a kicker.

    So for the people at NEAR, wish them good hunting. But if they find anything where we would like to see it, that might be against some high odds.

    As mentioned above, since those engaged in celestial mechanics, including astrodynamics, emphasize the mathematical nature of three body problems and how to solve them, when I identified some stars where the prospects for terrestrial orbits were not favorable, the most intense discussion came about how to calculate more precisely the points at which the system goes into chaos. A couple of people had recommendations for more precise integration techniques. All very well for accuracy’s sake, but existence on this planet probably owes or is connected more to the relatively simple means it takes to predict where the planet will be next week or in a million years. Someday perhaps I will be able to simulate the failure cases more accurately – and write a better post mortem.

  • Ronald June 13, 2019, 5:01

    Related paper just out:
    Nielsen et al. The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au.
    http://dx.doi.org/10.3847/1538-3881/ab16e9

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