by Paul Gilster | Feb 21, 2014 | Culture and Society |
If human civilization is to extend itself beyond our planet, it will need to take with it the plants, animals and microorganisms that can sustain a living ecosystem. Nick Nielsen argues in this compelling essay that preserving our own species into the remote future thus means preserving terrestrial biology as well, drawing sustenance from it and maintaining it long enough for Earthly systems — and ourselves — to evolve in the myriad environments that await us among the stars. Mr. Nielsen’s examination of future speciation continues his ongoing series on existential risk and the nature of human expansion. You can keep up with his thinking on his two blogs: Grand Strategy: The View from Oregon and Grand Strategy Annex, or follow him on Twitter, where he is @geopolicraticus.
by J. N. Nielsen
Some time ago on Twitter I wrote, “Astrobiology is island biogeography writ large.” As in the classic science fiction film This Island Earth, we know our world to be an island oasis of life in the midst of a dark and possibly barren cosmic ocean of space. Astrobiology, in seeking to understand the place of life in the universe, seeks to understand our oasis of life in a cosmological context. Perhaps we will be forced to reconcile ourselves with an unrelieved cosmic loneliness; perhaps we will find that life is plentiful in the universe; perhaps life will be found to be so plentiful that it seems likely that life on earth is a consequence of panspermia. Whatever the result of our search, whatever remarkable discoveries we make, complex multicellular life like ourselves is likely to require some kind of homeworld for its initial evolution, and these worlds are likely to be distributed across widely separated worlds. Astrobiology is the cosmic biogeography that can serve as the field guide to this archipelago of habitable worlds.
The existence of galactic habitable zones (GHZ) and circumstellar habitable zones (CHZ) [1] implies regions of greater and lesser habitability, and the distribution of stars, planets, moons and other matter within the GHZ and CHZ implies worlds of greater and lesser habitability. A recent paper on Superhabitable Worlds [2] has suggested that there may be planets or planetary systems more clement to life than the environment of Earth. This implies the possibility that, although Earth looks like a unique oasis in the darkness of space, it may represent a cosmic region of sub-optimal habitability. At very least, we have much to learn about habitability, given the present necessity of extrapolating from a single data point. It seems, however, than in spite of our ignorance of life elsewhere in the cosmos we must first attempt to map the habitable zones of the universe if we are to search for the life that would supervene upon these habitable zones. The resulting patterns of habitability and life that we will eventually be able to map will be our biogeography of the cosmos – a kind of biocosmography or bioastrography – and we will want to consider the relationship between forms of life that occur at nodal points of habitability, if there are any such relationships.
Biogeographers in discussions of species distribution distinguish between stepping-stones routes, single-step routes, and sweepstakes routes of species dispersal. A stepping-stones route is a gradual process that is integral with the evolution of a species, which expands its range as its population grows, slowly covering a landscape. A single-step route is when, “organisms cross a barrier in a direct, single event, not sequentially.” [3] A sweepstakes route is dispersal via a vector that is rare and unusual. Many islands are eventually colonized by sweepstakes routes, which accounts for their distinctive flora and fauna. A lizard that happens to ride a floating log to an island and finds another lizard of the same species with which to perpetuate the species has experienced a sweepstakes dispersal route. Mostly on islands, one finds insects and birds and marine mammals, and few larger species that cannot fly or swim to the island under their own power.
Astrobiology will need to make similar distinctions among cosmological stepping-stones routes, single-step routes, and sweepstakes routes. We have already begun to understand some of the potential dispersal vectors. We know that a certain amount of matter is exchanged between the planets of our solar system, and it is possible that microorganisms have hitched a ride between planets on rocks blasted off the surface of a planet by some enormous impact. Under conditions prevailing in our solar system, however, we cannot expect that complex multicellular life could expand from our homeworld in this way.
In a superhabitable world or solar system, as noted above, it might be possible for complex, multicellular organisms to follow a stepping-stones route to dispersal beyond their homeworld, and thereby attain a far higher degree of existential viability than they would enjoy if they had remained an autochthonous species of a single celestial body. Apart from superhabitable worlds, on sub-optimally habitable worlds the scenario of single-celled microorganisms living on a piece of ejected debris that eventually finds itself on a celestial body other than its homeworld would constitute a paradigm case of a sweepstakes route.
It is possible to imagine circumstances of superhabitable worlds or even superhabitable solar systems in which the means provided by industrial-technological civilization are not necessary to the dispersal of life to other worlds, and a single-step route may be facilitated by naturally occurring means. In our perhaps sub-optimally habitable solar system, however, this is not possible. For the complex, multicellular life that we know and love on Earth, the only method of extraterrestrial dispersion would be a single-step route, the only dispersal vector would be a spacecraft, and the only way to produce a spacecraft is through a relatively advanced industrial-technological civilization.
Thus the long term existential viability of the terrestrial biosphere is predicated upon the growth and expansion of industrial-technological civilization, which seems paradoxical. In the early stages of industrial-technological civilization, up to and including the present day, the expansion of industrial-technological civilization has come at a cost to the terrestrial biosphere. It has even been suggested that another mass extinction is taking place, an anthropogenic mass extinction, as a result of human activity on Earth. Nevertheless, a vital technological civilization is, at least in our solar system, a necessary prerequisite to the survival of any life derived from the terrestrial biosphere once the Earth passes its natural span of habitability.
It is not only human beings that benefit from space travel and settlement; existential risk mitigation affects every living thing on Earth. If human beings establish a permanent and self-sustaining presence off the surface of the Earth, such an outpost of terrestrial life could only achieve a self-sustaining ecosystem through the parallel presence of thousands if not millions of other terrestrial species (keeping in mind that the majority of these species will be microorganisms, millions of terrestrial species do not necessarily impose insuperable spatial requirements for an off-world settlement). When we go into space, we must take with us the plants and animals that we eat or otherwise rely upon for our existential viability.
If we fail to utilize the resources of our industrial-technological civilization to lift ourselves and our fellow terrestrial species off the Earth, all that has been achieved by the terrestrial biosphere will be lost (i.e., it is not only humanity and civilization that are lost should we succumb to existential risk), except for the possibility of some extremophile microorganisms that might ultimately survive the dissolution of the Earth’s biosphere if blasted into space.
The natural lifespan of the Earth will eventually lapse and come to an end, and after that the natural lifespan of the sun, too, will be exhausted and lapse, which is why Wernher von Braun said, “The importance of the space program is to build a bridge to the stars, so that when the Sun dies, humanity will not die. The Sun is a star that’s burning up, and when it finally burns up, there will be no Earth… no Mars… no Jupiter.” [4] While his expression of the idea is anthropocentric, we can see that any bridge to the stars must also be a bridge for other terrestrial species as well as ourselves. In short, interstellar travel is a dispersal vector for terrestrial biology.
Once our terrestrial biology is extended to other worlds – initially, other worlds in our solar system, and then other worlds orbiting other stars – it will be subject to unprecedented selection pressures, and in the long term these selection pressures will result in speciation specific to the new environments in which terrestrial species gain a foothold. In other words, terrestrial life will continue to evolve, and it will evolve on other worlds in a way that it does not and would not evolve on Earth. Speciation on a cosmic scale will be the result. We do not know and cannot predict the direction that life will take in its adaptive radiation throughout the cosmos.
It will not be until the first terrestrial seeds are planted in lunar soil in a greenhouse on the moon, or in Martian soil in a greenhouse on Mars, that we will know what terrestrial plants grow well in these soils and under these conditions. Only experience can teach us this, as the interaction of organism and environment, especially under novel conditions, is too complex to predict with certainty, and life is a paradigm of contingency, subject to the thousand natural shocks that flesh is heir to.
If this ignorance of the consequences of space settlement for our own biology sounds like I am making light of our knowledge and abilities – after all, human beings have been farmers for more than ten thousand years – the idea is precisely analogous to another challenge faced by space travel. We do not yet know, and cannot predict on the basis of present knowledge of science, technology, and engineering, what technologies will prove to be the most robust forms of propulsion for interstellar vessels. Among the many concepts for interstellar propulsion that have been proposed there remains not only all the science yet to be done to confirm or invalidate the concept, but also the building of specific technologies on the basis of this science, engineering particular vehicles employing these specific technologies, and then the testing and proving of these vehicles in the kind of conditions that will only be faced in flight. In the same way, we do not yet know what terrestrial plants and animals will prove to be robust partners in space exploration.
We may eventually treat our food supply and sustainable ecosystem as an engineering problem, but that will compound rather than limit the unknowns of speciation. Because of our anthropocentric moral standards, we will likely have less moral compunction about modifying other species for their use on space settlements or other worlds; even then, species modified for our use in artificial environments (i.e., on shipboard and space settlements) or on other worlds (initially, Mars and moons in our solar system, and then other planets around other stars) will be subject to a twofold selection process that is only likely to accelerate their adaptive radiation, viz. these two selection pressures being the artificial selection resulting from human genetic engineering of other species and the natural selection of novel environments not encountered by any terrestrial species that remains on Earth.
Notes
[1] Cf. e.g., Astrobiology of Earth: The emergence, evolution, and future of life on a planet in turmoil, Joseph Gale, Oxford: Oxford University Press, 2009, p. 33
[2] Superhabitable Worlds, Heller, René and Armstrong, John. Astrobiology. January 2014, 14 (1): 50-66. doi:10.1089/ast.2013.1088.
[3] Trans-oceanic dispersal and evolution of early composites (Asteraceae) Liliana Katinas, Jorge V. Crisci, Peter Hoch, Maria C. Tellería, María J. Apodaca, Perspectives in Plant Ecology, Evolution and Systematics, Volume 15, Issue 5, 20 October 2013, Pages 269-280
[4] This was quoted by Friedwardt Winterberg at the Icarus Interstellar Starship Congress, Day 2; I have been unable to locate a source for this quote.
by Paul Gilster | Feb 20, 2014 | Exoplanetary Science |
Following up on yesterday’s post on Gaia, it seems a good time to discuss PLATO, the European Space Agency’s planet hunting mission, which has just been selected for launch by ESA’s Science Policy Committee. The agency’s Cosmic Vision program has already selected the Euclid mission to study dark energy (launch in 2020) and Solar Orbiter, an interesting attempt to study the solar wind from less than fifty million kilometers. Solar Orbiter will surely return data we’ll want to discuss here in terms of magsails, electric sails and other ways to harness a solar wind about which we have much to learn.
Solar Orbiter’s launch is the closest of the three, scheduled for 2017, with PLATO pegged for 2024, the launch to be from the European spaceport in Kourou (French Guiana) aboard a Soyuz booster. Note that date, because it’s expected, as this BBC story notes, that the ground-based European Extremely Large Telescope (E-ELT) will be operational in Chile by 2024, a reminder that it should be powerful enough, with its 39-meter primary mirror, to carry out studies of planetary atmospheres as determined by targets PLATO can provide.
The mission will operate from the L2 Lagrangian point 1.5 million kilometers from the Earth, from which vantage PLATO will turn 34 individual telescopes and cameras on to a field of view that encompasses half the sky. Up to a million stars will be under investigation, looking for the characteristic lightcurve of a planet transiting the star as seen from Earth. PLATO will also have a strong asteroseismology component, allowing even more precision in characterizing its planetary finds, especially since these will be followed up with ground-based radial velocity observations that will benefit from having data on surface pulsations on target stars.
Thus PLATO’s unravelled acronym: PLAnetary Transits and Oscillations of stars. The ultimate goals are exactly those we’d expect: To discover and characterize relatively nearby planetary systems, detecting Earth-sized planets and ‘super-Earths’ in the habitable zone around solar-type stars while measuring solar oscillations in the host stars. Working at optical wavelengths, PLATO should be able to determine planetary mass with a precision of 10 percent, planetary radius with a precision of 2 percent and stellar age up to 10 percent.
The BBC quotes Don Pollacco (University of Warwick, leader of the PLATO Science Consortium), on how the mission differs from those that have gone before:
“PLATO will be our first attempt to find nearby habitable planets around Sun-like stars that we can actually examine in sufficient detail to look for life. Nearly all the small transiting planets discovered so far have been beyond our technology to characterise. PLATO will be a game-changer, allowing many Earth-like planets to be detected and confirmed and their atmospheres examined for signs of life.”
The contrast is, of course, with Kepler, whose stars — in a magnitude range between 7 and 17 — were faint enough that follow-up studies for the majority of candidates are difficult if not impossible. The interesting Lost in Transits blog, written by a PhD student at the University of Warwick and thus likely connected with Don Pollacco at the same school, points out that Kepler’s wide field and large camera array will be turned to brighter stars (magnitude 4-16) with equipment sufficient to follow up even small Earth-class planets around these stars. The blog also points to the effectiveness of asteroseismology in this work:
This ability to survey bright stars also allows astronomers to perform extremely sensitive measurements of the stars themselves. By using variations in starlight caused by ripples on the star’s surface, astronomers can accurately pin down not only the size of the star but also the age of the star system. This means, not only can Plato find exoplanets around bright stars, but it can also determine the size and age of many of these planets to a precision only previously dreamed of.
Ahead for PLATO are further refinements and finalization of the design, along with selection of an industrial prime contractor and, within the next two years, the final adoption of the mission, but the support given by the ESA Science Policy Committee, unanimous, strengthens our hopes that PLATO will fly. The fudge factor in that statement simply reflects the disappointments we’ve seen on both sides of the Atlantic with missions like SIM (Space Interferometry Mission) and the Darwin astronomical interferometer all showing promise only to face cancellation. Budgetary realities are always to be reckoned with, but PLATO’s selection is welcome news indeed.
For more detail on PLATO, see Rauer et al., “The PLATO 2.0 Mission” (abstract).
by Paul Gilster | Feb 19, 2014 | Exoplanetary Science |
The young star known as L1527 offers a spectacular view at infrared wavelengths, a result of the configuration of gas and dust around it. Have a look at the image below, taken by the Spitzer Space Telescope, where light from the star escapes through the opening provided by a bipolar gas flow, illuminating the gas to highlight a nebula in the shape of a butterfly. Earlier radio studies of this star have shown that L1527 is surrounded by a gas disk that, from our perspective, is seen edge-on. Now new radio observations are helping us characterize the gas itself.
Image: An infrared image of the protostar L1527 taken by the Spitzer Space Telescope. Credit: J. Tobin/NASA/JPL-Caltech.
It’s an interesting investigation because the chemical changes inside a disk as it forms are little understood. Intense observational effort has gone into studying the physical structure of protoplanetary disks, but separating the young disk and the infalling envelope of gas and dust that gives rise to it is difficult. This is where the powerful sensitivity of ALMA (Atacama Large Millimeter/submillimeter Array, a radio interferometer array in Chile’s Atacama desert) may come to our aid. The new work, described in this news release from the University of Tokyo, is built around ALMA’s high spatial resolution observations to study the chemistry of disk formation.
Invisible in infrared light, the gas around L1527 can be readily examined at ALMA’s wavelengths, its molecules characterized in terms of their density, temperature and chemical composition. Researchers under Nami Sakai (University of Tokyo) have been studying the radio emission from cyclic-C3H2 (three carbon atoms in a loop-like structure with two hydrogen atoms attached) and sulfur monoxide (SO) molecules — these are emissions weak enough to be undetectable by other instruments, but within range of the ALMA array.
Because a new stellar system is formed through the gravitational collapse of interstellar materials, you would think that the interstellar gas and dust would simply be incorporated into the new disk structure as is. But Sakai and team have found something different: There is a chemical change associated with the formation of the disk. L1527’s disk has a radius of about 500 AU. Inside 100 AU, the emission from cyclic-C3H2 is weak enough to suggest chemical differentiation between the inner and outer disk. Meanwhile, SO seems to be concentrated in a ring-like structure with a radius of about 100 AU. The image below shows the result.
Image: L1527 observed by Spitzer (Left) and the distributions of cyclic-C3H2 (center) and SO (right) observed by ALMA. ALMA reveals the gas distribution just close to the protostar. Emission from cyclic-C3H2 is weak toward the protostar but strong at the northern and southern parts. Meanwhile, SO has its emission peak near the protostar. Credit: J. Tobin/NASA/JPL-Caltech, N. Sakai/The University of Tokyo.
So we have a striking change in chemical composition about 100 AU out. Sakai’s simulations show that infalling gas from the outer parts of the disk is piling up at what he calls the ‘centrifugal barrier.’ Local heating in this region as the infalling gas accumulates causes distinct chemical changes. Here I’m going to quote Masaaki Hiramatsu (NAOJ Chile Observatory), who put together a backgrounder on Sakai’s work, describing the lively action around this ‘barrier’:
The infalling gas collides with the barrier and is warmed up. SO molecules frozen on the surface of cold dust grains are liberated into the gas phase. The temperature decreases inside the barrier and the SO molecules are frozen again. This is the formation process of the SO ring at 100 AU. Rotating motion dominates inside the centrifugal barrier. Hence, the barrier is the edge of the disk formation region in which eventually a planetary system will be formed.
I’m not aware of earlier work on the chemical differences between protoplanetary disks and the interstellar clouds out of which they form, or of any earlier evidence for major changes in the chemistry of the disk as it emerges. It’s worth asking whether similar situations will be traced in other protoplanetary disks, something that only future observation will tell us, with inevitable implications for how our own Solar System formed if this turns out to be a common process. The paper suggests that micro-analyses of meteorites, spectroscopy of comets, and sample return from the asteroids will help us extend this study to our own system’s formation.
The paper is Sakai et al., “Change in the chemical composition of infalling gas forming a disk around a protostar,” published online in Nature 12 February 2014 (abstract).
by Paul Gilster | Feb 18, 2014 | Deep Sky Astronomy & Telescopes |
We have several months yet before the European Space Agency’s Gaia mission enters its five-year operational phase. But you can see an important milestone in the image below. Gaia’s two telescopes have to be aligned and focused as its other instruments are calibrated. Testing involves downloading data like this image of NGC1818, a young star cluster in the Large Magellanic Cloud. The image covers an area something less than one percent of the spacecraft’s full field of view. Launched on December 19, 2013, Gaia now orbits around the L2 Lagrangian point some 1.5 million kilometers from Earth.
Image: A calibration image from Gaia is part of early testing of the mission’s systems. Credit: ESA/DPAC/Airbus DS.
Gaia inevitably makes me think of Hipparcos, an earlier ESA mission launched in 1989 devoted to precision astrometry, the measurement of proper motions and parallaxes of stars to help us figure out their distance and tangential velocity. What a far cry Hipparcos was from the days when Thomas Henderson, then observing at the Cape of Good Hope, was trying to measure the parallax of Alpha Centauri, all the while dueling with the German astronomer Friedrich Wilhelm Bessel to demonstrate that the method could give us a distance measurement to a star.
Bessel’s work on 61 Cygni took precedence but both astronomers proved that the closest stars could be measured using the instruments of their day. But measuring star positions from the ground has always been tough thanks to atmospheric effects and instrument limitations. And as we looked further and further from our own stellar neighborhood, these methods grew more challenging still, which is why proposals for a space mission devoted to astrometry began as early as 1967. The Hipparcos Catalog was released in 1997, covering precise measurements of almost 120,000 stars, with less precise readings on about a million more.
Now we have Gaia, which will chart 10,000 times as many stars as Hipparcos, with measurements of their position and motion that are 100 times more accurate. If all goes well, we should wind up with the largest three-dimensional map of the Galaxy ever created, charting one billion stars in terms of their distribution, brightness, temperature, composition and motion. Gaia should firm up our understanding of galactic structure while making numerous exoplanet finds and uncovering vast numbers of brown dwarfs. We can expect measurements of 500,000 quasars in the distant universe and, much closer to home, data on new asteroids.
It’s an ambitious mission, one that contains twin optical telescopes and their imaging system, a radial velocity spectrometer and blue/red photometers. The telescopes will focus their light onto a 106 CCD focal plane array with almost one billion pixels, making Gaia’s the largest digital camera yet deployed in space. The two telescopes will monitor each target star about 70 times over the five year mission, sweeping the entire sky in the process, their repeated measurements teasing out the parallax and true motion of each object. Objects down to magnitude 20 are in range, and according to this ESA backgrounder, the accuracy will range from 20 percent for stars near galactic center to 0.001 percent for stars closest to the Solar System.
Every one of Gaia’s billion stars will have been observed in the first six months of operations once calibrations are completed, but it’s the repeated observations over five years that will allow accurate determination of stellar distances and motion, with the final catalog not scheduled to be released until three years after the end of the mission. We need to keep a close eye on Gaia. It is essentially bringing our fuzzy maps of the Milky Way into much higher resolution, with implications for existing work like Kepler’s — Gaia will be able to give us accurate information about distance and motion for the planet-bearing systems Kepler has thus far found. A million gigabytes of data are in store as Gaia’s enormous catalog deepens our view of the galaxy.
by Paul Gilster | Feb 17, 2014 | Asteroid and Comet Deflection |
It was just a year ago, on February 15, 2013, that the 30-meter asteroid 2012 DA14 whisked past the Earth at a distance of well less than 30,000 kilometers, inside the orbits of our geosynchronous satellites. If you don’t recall 2012 DA14, it’s probably because it was later on the same day that the Chelyabinsk impactor struck, a 20-meter asteroid that released the energy of approximately 460 kilotons of TNT. Chelyabinsk made it into 2014 Olympic news at Sochi, with ten gold medals for February 15 winners being embedded with fragments from the object.
Today we get the passage of near-Earth asteroid 2000 EM26, whose closest approach will be covered by the Slooh network of automated telescopes starting at 2100 EST (0200 UTC), live from the Canary Islands. An iPad app is available or you can watch on Slooh.com, with the live image stream accompanied by commentary from astronomer Bob Berman and guests discussing the event and fielding questions from viewers using the hashtag #asteroid. Berman notes the significance of asteroid tracking and developing future mitigation strategies:
“On a practical level, a previously-unknown, undiscovered asteroid seems to hit our planet and cause damage or injury once a century or so, as we witnessed on June 20, 1908, and February 15, 2013. Every few centuries, an even more massive asteroid strikes us — fortunately usually impacting in an ocean or wasteland such an Antarctica. But the ongoing threat, and the fact that biosphere-altering events remain a real if small annual possibility, suggests that discovering and tracking all NEOs, as well as setting up contingency plans for deflecting them on short notice should the need arise, would be a wise use of resources.”
The Challenge of Asteroid Capture
With almost 11,000 near-Earth objects now discovered, the astronomical community continues its work on planetary defense. The Asteroid Redirect Mission (ARM) is NASA’s bid to find a small asteroid that can be parked in a lunar orbit for study and thorough exploration in the 2020s. This JPL news release gives us more information about ARM’s current status, noting two possible scenarios: An entire small asteroid could be captured and redirected into lunar orbit, or a large boulder or other mass from a larger asteroid could be retrieved and put into a similar orbit.
Image: This concept image shows an astronaut preparing to take samples from the captured asteroid after it has been relocated to a stable orbit in the Earth-moon system. Hundreds of rings are affixed to the asteroid capture bag, helping the astronaut carefully navigate the surface. Credit: NASA/JPL.
But finding the right asteroid is tricky business. Most near-Earth asteroids are either too large or in unsuitable orbits, and would-be targets can move out of range of our instruments so fast that it becomes a challenge to get enough data to make the call. The goal is something smaller than about twelve meters across, says Paul Chodas, a senior scientist in the Near-Earth Object Program Office at JPL. He adds: “There are hundreds of millions of objects out there in this size range, but they are small and don’t reflect a lot of sunlight, so they can be hard to spot. The best time to discover them is when they are brightest, when they are close to Earth.”
The news release goes through the detection and analysis process. The coordinates of objects detected by asteroid surveys flow to the Minor Planet Center in Cambridge, MA, where the objects can be tagged as previously known or else given a new designation. Orbit, intrinsic brightness and other data are then refined by the Near-Earth Object Program Office at JPL, which updates its online small body database. Now in place for the projected asteroid redirect mission is a new screening process that scans for candidate objects.
Radar observations by the Deep Space Network at Goldstone (CA) or Arecibo Observatory in Puerto Rico can produce further data on orbit and size if they are able to track the asteroid, but other observatories both professional and amateur may also be asked to look at it. The Infrared Telescope Facility at Mauna Kea can provide details on spectral type, reflectivity and likely composition. Several dozen 6- to 12-meter asteroids are thought to fly by the Earth at a distance closer than the Moon every year, but few of these are in suitable orbits for the ARM mission.
Even so, the wave of new technology now approaching should make finding the right object a sure thing. Lindley Johnson (Near-Earth Objects Program, NASA headquarters) notes what we can expect:
“The NASA-funded Catalina Sky Survey, which has made the majority of NEO discoveries since its inception in 2004, is getting an upgrade. We also will have new telescopes with an upgraded detection capability, like PanSTARRS 2 and ATLAS, coming online soon, and the Defense Advanced Research Projects Agency’s new Space Surveillance Telescope will give us a hand as well.”
And don’t forget our old friend WISE, which I usually write about in terms of brown dwarfs in the Sun’s vicinity. The repurposed spacecraft now functions as NEOWISE and may help in characterizing targets for the redirect mission.
Potential candidates are being flagged at the rate of about two per year, a number that is bound to climb as these further resources come into play. We’ll then have a target and a plan as we proceed in our efforts to characterize these objects. NASA is assuming that an Orion spacecraft and Space Launch System (SLS) rocket will make asteroid capture happen, but whatever the hardware, studying small asteroids up close — and ultimately developing strategies for nudging the trajectories of much larger objects — is a vital part of future planetary defense.
