Centauri Dreams
Imagining and Planning Interstellar Exploration
Lucy in the Sky
Extended operations at multiple targets, as Dawn showed us, are possible with ion propulsion. But we still learn much from flybys, something New Horizons reminded us with its spectacular success at Pluto/Charon, and again reminds us as it closes on MU69. Likewise, a mission called Lucy will visit multiple objects, using traditional chemical propulsion with gravity assist to achieve flybys of seven different targets. The destination: Jupiter’s trojan asteroids. With launch scheduled for 2021, Lucy’s will study six Jupiter trojans and one asteroid in the Main Belt.
Image: Jupiter’s extensive trojan asteroids, divided into ‘Trojans’ and ‘Greeks’ in a nod to Homer, but all trojans nonetheless. Credit: “InnerSolarSystem-en” by Mdf at English Wikipedia – Transferred from en.wikipedia to Commons. Licensed under Public Domain via Commons.
The trojans are interesting bodies orbiting at the L4 and L5 Lagrange points 60° ahead and behind the gas giant. Jupiter’s trojans are the best known but the term is generic — Neptune has trojans, as does Mars, Uranus and even the Earth (2010 TK7). In fact, some Solar System moons themselves have trojans, as we saw recently when discussing Saturn’s moon Dione, which has the trojans Helene and Polydeuces. Saturn’s moon Tethys also has two trojans.
But as befits Jupiter’s massive size, it’s associated with over 6000 trojans already identified, and a larger population perhaps reaching as high as one million objects over a kilometer in diameter. 617 Patroclus is a particularly intriguing object, a D-type asteroid thought to have water ice in its interior. This object is actually a binary, with a moon named Menoetius slightly smaller than the primary. But we have C- and P- type asteroids in these Lagrange points as well, and Lucy will give us a view of each type as it makes its way into both clusters of Trojans.
The assumption is that the Jupiter trojans are remnants of primordial planet-building material, with clues to the Solar System’s formation and possibly the origins of organic material on Earth. While C-type asteroids are primarily found in the outer regions of the Main Belt, the darker P- and D-type objects have similarities to Kuiper Belt objects beyond the orbit of Neptune. Evidently abundant in dark carbon compounds, all are thought to be rich in volatiles.
Image: This diagram illustrates Lucy’s orbital path. The spacecraft’s path (green) is shown in a frame of reference where Jupiter remains stationary, giving the trajectory its pretzel-like shape. After launch in October 2021, Lucy has two close Earth flybys before encountering its Trojan targets. In the L4 cloud Lucy will fly by (3548) Eurybates (white), (15094) Polymele (pink), (11351) Leucus (red), and (21900) Orus (red) from 2027-2028. After diving past Earth again Lucy will visit the L5 cloud and encounter the (617) Patroclus-Menoetius binary (pink) in 2033. As a bonus, in 2025 on the way to the L4, Lucy flies by a small Main Belt asteroid, (52246) Donaldjohanson (white), named for the discoverer of the Lucy fossil. After flying by the Patroclus-Menoetius binary in 2033, Lucy will continue cycling between the two Trojan clouds every six years. Credits: Southwest Research Institute.
The Lucy mission has just passed the milestone known as Key Decision Point C, a confirmation review that authorizes continuation of the project into its development phase and sets its cost and schedule. This means as well that the confirmation review panel has approved the instrument suite, budget and risk factor analysis for the overall mission. Up next comes the Critical Design Review, which thoroughly vets all aspects of the system design.
Lucy, in other words, is well on its way, says principal investigator Hal Levison (SwRI):
“Up until now this mission has entirely been on paper. Now we have the go ahead to actually cut metal and start putting this spacecraft together.”
Emphasizing the connection with the origins of the Solar System and the possible delivery of organics to Earth, PI Levison named the mission after Lucy, the fossil remains of a three million year old hominid. But he’s enough of a Beatles fan to see a connection there as well, as noted in an older quote on the mission:
“These asteroids really are like diamonds in the sky in terms of their scientific value for understanding how the giant planets formed and the solar system evolved.”
Including imaging and mapping instruments — a color imaging and infrared mapping spectrometer, a high-resolution visible imager, and a thermal infrared spectrometer — the science instrument package is similar to what flew on New Horizons and OSIRIS-REx. Lucy should reach its first targets, the L4 trojans, in 2025, followed by a return to Earth and gravity assist there to move on to the L5 trojan cluster in 2033, The craft will also make a flyby of Main Belt asteroid 52246 Donaldjohanson, which was named for the discoverer of the Lucy fossil.
Parker Solar Probe: Already a Record Setter
Over the sound system in the grocery store yesterday, a local radio station was recapping events of the day as I shopped. The newsreader came to an item about the Parker Solar Probe, then misread the text and came out with “The probe skimmed just 15 miles from the Sun’s surface.” Yipes!
I was in the vegetable section but you could hear him all over the store, so I glanced around to see how people had reacted. Nobody as much as raised an eyebrow, which either says people tune out background noise as they shop or they have little knowledge of our star.
The correct number is 15 million miles (24,1 million kilometers), and it’s still a hugely impressive feat, but I hope the station got the story right later on. I go easy on this kind of thing because it’s easy enough to make a mistake when reading radio copy (I’ve done this myself). Anyway, there is always some listener who calls it in, which I should have but didn’t. I was pushed for time that morning, making choices about squash and rutabagas and thinking about close approaches.
Image: Artist’s concept of the Parker Solar Probe spacecraft approaching the sun. The spacecraft will provide new data on solar activity and make critical contributions to our ability to forecast major space-weather events that impact life on Earth. Credit: NASA/JHU/APL.
After the Parker Solar Probe’s close pass, the spacecraft has gone nearer the Sun than any other craft. The Helios B probe was the previous recorder holder, setting the mark back in 1976. Helios B reached perihelion in April of 1976 at a distance of 43.4 million kilometers (26.9 million miles), inside the orbit of Mercury. A record the Parker probe surpassed with ease.
And the good news about Parker, reflected in the faces in the image below, is that the craft handled the heat and solar radiation without damage. Four status beacon signals are available, the best being the A signal that was received by mission controllers at JHU/APL on the late afternoon of November 7. Our latest mission to the Sun is live and collecting data.
Image: Members of the Parker Solar Probe mission team celebrate on Nov. 7, 2018, after receiving a beacon indicating the spacecraft is in good health following its first perihelion. Credit: NASA/Johns Hopkins APL/Ed Whitman.
Parker is also setting speed records. Again we turn to Helios-B as the previous record-holder, at 70.2 km/s (157,078 mph). At perihelion on November 7, the Parker spacecraft reached 213,200 miles per hour, or 95.3 kilometers per second. By way of comparison, Voyager 1 moves at approximately 17 kilometers per second as it continues to push into interstellar space. Still in the heliosheath, sister spacecraft Voyager 2 is at a slightly more sedate 15.4 km/sec.
But back to the Parker Solar Probe, whose Sun-facing Thermal Protection System, an 11-centimeter thick carbon-carbon composite shield, reached about 820 degrees Fahrenheit, or 437 degrees Celsius. This is just the beginning, for the spacecraft will continue making closer and closer approaches in the course of its 7-year mission. 24 passes by the Sun are anticipated. The spacecraft will eventually close to a scorching 6.2 million kilometers from our star.
Deep space implications? The Parker Solar Probe’s findings will teach us much about the plasma flow leaving the Sun, a solar ‘wind’ that may offer future magnetic sails (magsails) one option for reaching high velocities within the Solar System (though we first must determine whether this highly variable flow can be efficiently exploited by future magsail designs).
The other implication is using a close solar pass in a ‘sundiver’ mission, accelerating a large payload that would be flung outbound in a spectacular gravitational assist, reaching velocities in the hundreds of kilometers per second. We’ll gain a great deal of knowledge about operations close to the Sun through the performance of Parker’s heat shield, all of which should be helpful if we do decide to explore sundiver options for reaching into the Kuiper Belt and beyond.
Fine-Tuning Mechanisms for Water Delivery
We’ve long been interested in how the Earth got its oceans, with possible purveyors being comets and asteroids. The idea trades on the numerous impacts that occurred particularly during the Late Heavy Bombardment some 4.1 to 3.8 billion years ago. Tuning up our understanding of water delivery is important not only for our view of our planet’s development but for its implications in exoplanet systems with a variety of different initial conditions.
Image: This view of Earth’s horizon was taken by an Expedition 7 crewmember onboard the International Space Station, using a wide-angle lens while the Station was over the Pacific Ocean. Credit: NASA.
But the picture becomes more complex when we compare regular hydrogen atoms (one proton, one electron) with ‘heavy hydrogen,’ or deuterium atoms. The latter have a neutron in addition to a proton in the nucleus. A recent paper in the Journal of Geophysical Research digs into isotope ratios, the ratio of deuterium to ordinary hydrogen atoms, commonly referred to as the D/H ratio. One reason asteroids are favored by some scientists as the likely source of the bulk of Earth’s water is that asteroidal water has a D/H in the neighborhood of 140 parts per million. Contrast that with cometary water, which runs from 150 ppm to as high as 300 ppm.
When we examine Earth’s oceans, we find a D/H ratio close to that found in asteroids. The new study, from Jun Wu and colleagues at the School of Molecular Sciences and School of Earth and Space Exploration at Arizona State University, takes aim at the asteroid explanation, not by way of discounting it but rather of finding other sources making a contribution to Earth’s water.
“It’s a bit of a blind spot in the community,” said ASU’s Steven Desch, a co-author of the new study. “When people measure the [deuterium-to-hydrogen] ratio in ocean water and they see that it is pretty close to what we see in asteroids, it was always easy to believe it all came from asteroids.”
We are learning, however, that too uncritical an acceptance of D/H ratios may oversimplify the issue. For the hydrogen in Earth’s oceans is not necessarily representative of hydrogen deeper inside the planet, where D/H ratios close to the boundary between the core and mantle show considerably less deuterium. This may indicate a non-asteroidal source for at least some of the hydrogen.
Another telling point is that helium and neon, showing isotopic signatures inherited from the original solar nebula, have also been found in Earth’s mantle. Contrasting hydrogen at the core-mantle boundary with what we see in Earth’s oceans and factoring in these noble gases may change our thinking. The Wu study considers the formation of the planets in the earliest days of the Solar System, when small, often colliding planetary embryos up to the size of Mars went through gradual planetary accretion.
The new model works like this: As larger embryos formed largely from water-laden asteroids, they began to develop into planets. On Earth, decaying radioactive elements melted iron within the emerging world, pulling in asteroidal hydrogen and sinking to form a core. Collisions among planetesimals would meanwhile have created enough energy to melt the surfaces of the larger embryos like the Earth into magma oceans.
Hydrogen and noble gases from the solar nebula would be drawn in to create an early atmosphere. The nebular hydrogen, lighter than asteroidal hydrogen, would have dissolved into the molten iron of the magma ocean, eventually being drawn into the mantle, along with hydrogen from other sources.
What the authors argue is that this process created a slight enrichment of hydrogen in the molten iron and left a higher ratio of deuterium behind in the magma (the process is called isotopic fractionation). Hydrogen is attracted to iron, while the heavier isotope, deuterium, less attracted to iron, would have remained in the magma which would eventually become Earth’s mantle. We would end up with lower D/H ratios in the core than in the mantle and oceans. The authors argue that while most of Earth’s water is asteroidal, some of it did in fact come from the solar nebula.
The process is complex, and also takes in impacts from smaller embryos and other objects that continued to add water and mass until Earth reached its final size. The authors provide this synopsis as their caption for Figure 1 (above), which I’ll reproduce verbatim but break into sections for reasons of readability:
- (a) Earth accreted from embryos with chondritic [asteroidal] levels of water concentrations and D/H ratios.
- (b) These embryos differentiated and stored relatively light hydrogen in their cores, raising the D/H of hydrogen in their mantles.
- (c) The largest embryo accreted a proto-atmosphere and sustained a magma ocean into which nebular hydrogen diffused.
- (d) The largest embryo’s magma ocean crystallized and overturned, mixing light hydrogen into the mantle, but incompletely.
- (e) As smaller embryos were accreted, their mantles joined the proto?Earth’s mantle, and their cores merged with the proto?Earth’s core.
The result is:
- (f) Earth’s mantle today contains approximately three oceans of water in its mantle and surface, with average D/H ? 150 × 10?6, and ~4.8 oceans’ worth of hydrogen in its core, with D/H ? 130 × 10?6. Mantle plumes can sample low?D/H material from the core?mantle boundary.
Wu says this: “For every 100 molecules of Earth’s water, there are one or two coming from [the] solar nebula.” But we now see the potential for including gas left over from the formation of our Solar System in the question of water delivery and accumulation. In other stellar systems where water-bearing asteroids may not be as abundant, this implies that water could still be in place from the system’s own stellar nebula. Wu adds: “This model suggests that the inevitable formation of water would likely occur on any sufficiently large rocky exoplanets in extrasolar systems. I think this is very exciting.”
The paper concludes:
Our comprehensive model for the origin of Earth’s water considers, for the first time, the effects of isotopic fractionation as hydrogen dissolved into metal and was sequestered into the core. Based on the behaviors of proxies, we consider it likely that the D/H ratio of the core is ~10% lighter than the mantle. We hypothesize that Earth accreted a few to tens of oceans of water from chondrites, mostly carbonaceous chondrites. Drawing on the latest theories of planet formation, which argue for rapid (<2 Myr) formation of planetary embryos, we favor ingassing of a few tenths of an ocean of solar nebula hydrogen into the magma oceans of the embryos that formed Earth.
The paper is Wu et al., Journal of Geophysical Research: Planets 09 October 2018 (full text).
On the Earliest Stars
If you’ve given some thought to the Fermi question lately — and reading Milan ?irkovi?’s The Great Silence, I’ve been thinking about it quite a bit — then today’s story about an ancient star is of particular note. Fermi, you’ll recall, famously wanted to know why we didn’t see other civilizations, given the apparent potential for our galaxy to produce life elsewhere. Now a paper in The Astrophysical Journal adds punch to the question by making the case that the part of the galaxy in which we reside may be older than we have thought.
Finding that our Sun is younger than many nearby stars, an issue that Charles Lineweaver (Australian National University), among others, has examined, would allow even more time for civilizations to have emerged in the galactic neighborhood. But let’s now leave Fermi behind to look at the tiny star that prompts these ruminations (and to be sure, the paper on this star makes no mention of Fermi, but does tell us something quite interesting about the early cosmos).
Discovered by Kevin Schlaufman (Johns Hopkins University), 2MASS J18082002–5104378 B is the smaller of a binary pair that orbit a common barycenter. While the primary had been previously discovered, it was up to Schlaufman and team to uncover the far more interesting companion.
Schlaufman used data from the Magellan Clay Telescope, Las Campanas Observatory and the Gemini Observatory in finding and characterizing this star. What distinguishes 2MASS J18082002–5104378 B is its size, metallicity and age. On the latter, Schlaufman believes it could be as little as a single generation removed from the Big Bang itself, and the paper pegs its age at approximately 13.5 billion years. We’ve discovered other ancient stars with low metal content, but this one is located in the Milky Way’s thin disk, that part of the galaxy in which we reside. Hence the issue of the age of local stars, as the paper recounts:
Given its thin disk orbit, the 13.535 ± 0.002 Gyr age of the 2MASS J18082002–5104378 system provides a lower limit on the age of the thin disk. Similarly old but not quite as metal-poor stars have also been seen on thin disk orbits (e.g., Casagrande et al. 2011; Bensby et al. 2014). This is somewhat older than the 8–10 Gyr age of the thin disk suggested by classical studies of field stars (Edvardsson et al. 1993; Liu & Chaboyer 2000; Sandage et al. 2003), the white dwarf luminosity function (e.g., Oswalt et al. 1996; Leggett et al. 1998; Knox et al. 1999; Kilic et al. 2017), and the ages of the oldest disk open clusters Berkeley 17 and NGC 6791 (e.g., Krusberg & Chaboyer 2006; Brogaard et al. 2012).
Image: This edge-on diagram of the Milky Way shows the thin disk in green. Credit: Wikimedia Commons (CC BY-SA 3.0).
We are talking about a star with a content of metals roughly the same as the planet Mercury. Contrast that with the Sun, whose heavy element content is equal to approximately 14 Jupiters.
2MASS J18082002–5104378 B (here’s hoping it gets a new moniker, perhaps ‘Schlaufman’s Star’) is the lowest-mass ultra metal-poor star currently known. Yet despite its extreme age and low metallicity, it is found in the thin disk, and in fact is the most metal-poor star yet found that is part of the thin disk. We would expect stars forming not long after the Big Bang to be low in metals, given that hydrogen, helium and trace lithium are all they had to work with. It would be later stellar generations that could form with the heavier elements these early stars produced in their cores, seeding the cosmos with metals through supernovae explosions.
Call that first generation Population III stars, which when first modeled by researchers produced stars far more massive than the Sun, giant objects that should form as single stars in isolation. Later models dropped the range of mass to as low as 10 solar masses but also extended it on the high end. Low-mass Population III stars only recently began to be considered when the issue of fragmentation began appearing in numerical simulations. The discovery of 2MASS J18082002–5104378 B makes the case for the emergence of such stars.
From the paper:
We use models of protostellar disks around both UMP [low-mass ultra metal-poor] and Pop III protostars plus scaling relations for the fragment mass and migration time to argue that the existence of the low-mass UMP star 2MASS J18082002–5104378 B and the extremely metal-poor (EMP) brown dwarf HE 1523–0901 B discovered by Hansen et al. (2015) implies the survival of solar-mass fragments around Pop III stars…
Thus we may be looking at a new observable that can take us back to conditions at the earliest era of star formation:
Whereas fragmentation at the molecular core scale will likely lead to massive binary stars, the emergence of gravitationally bound solar-mass clumps in protostellar disks via gravitational instability has the potential to produce low-mass Pop III stars that may be observable in the Milky Way.
Image: The new discovery is only 14% the size of the Sun and is the new record holder for the star with the smallest complement of heavy elements. It has about the same heavy element complement as Mercury, the smallest planet in our solar system. Credit: Kevin Schlaufman/JHU.
Thus far about 30 stars considered ultra metal-poor have been identified, all of roughly the Sun’s mass, but 2MASS J18082002–5104378 B is only 14 percent of the Sun’s mass. The mass, incidentally, was determined by radial velocity methods, examining the wobble of the primary star. Backing out to the wider picture, our view of the earliest stars as extremely massive objects, unobservable to us because they would have burned quickly and died, has to be modified to include low-mass stars that can, at least in some situations, emerge, as 2MASS J18082002–5104378 B did, burning for long lifetimes indeed. Says Schlaufman:
“If our inference is correct, then low-mass stars that have a composition exclusively the outcome of the Big Bang can exist. Even though we have not yet found an object like that in our galaxy, it can exist.”
The paper is Schlaufman et al., “An Ultra Metal-poor Star Near the Hydrogen-burning Limit,” Astrophysical Journal Vol. 867, No. 2 (5 November 2018). Abstract / preprint.
SETI in the Infrared
One of the problems with optical SETI is interstellar extinction, the absorption and scattering of electromagnetic radiation. Extinction can play havoc with astronomical observations coping with gas and dust between the stars. The NIROSETI project (Near-Infrared Optical SETI) run by Shelley Wright (UC-San Diego) and team is a way around this problem. The NIROSETI instrument works at near-infrared wavelengths (1000 – 3500 nm), where extinction is far less of a problem. Consider infrared a ‘window’ through dust that would otherwise obscure the view, an advantage of particular interest for studies in the galactic plane.
Would an extraterrestrial civilization hoping to communicate with us choose infrared as the wavelength of choice? We can’t know, but considering its advantages, NIROSETI’s instrument, mounted on the Nickel 1-m telescope at Lick Observatory, is helping us gain coverage in this otherwise neglected (for SETI purposes) band. I had the chance to talk to Dr. Wright at one of the Breakthrough Discuss meetings in Palo Alto, where she made a fine presentation on the subject. Since then my curiosity about infrared SETI has remained high.
Meanwhile, at MIT…
Then this morning I came across graduate student James Clark, who has just published a paper on interstellar beacons in the infrared in the Astrophysical Journal. Working at MIT’s Department of Aeronautics and Astronautics, Clark is not affiliated with NIROSETI. He’s wondering what it would take to punch a signal through to another star, and concludes that a large infrared laser and a telescope through which to focus it would be the tools of choice.
The goal: An infrared signal at least 10 times greater than the Sun’s natural infrared emissions, one that would stand out in any routine astronomical observation of our star and demand further study. Clark believes that a 2-megawatt laser working in conjunction with a 30-meter telescope would produce a signal easily detectable at Proxima Centauri b, while a 1-megawatt laser working through a 45-meter telescope would produce a clear signal at TRAPPIST-1.
But nearby stars are just the beginning, for in Clark’s view, either of these setups would produce a signal that could be detected up to 20,000 light years away, almost to galactic center. All of this may remind you of Philip Lubin’s work, recently described here, on laser propulsion. Depending on the system in play, one of Lubin’s DE-STAR 4 beams would be observed as the brightest star in the sky from 1000 light years away (see Trillion Planet Survey Targets M-31 for more on this). The NIROSETI website makes the same observation about laser visibility:
The most powerful laser beams ever created (e.g. LFEX) can produce optical pulses with 2 petawatts (2.1015W) peak power for an incredibly short duration, approximately one picosecond. Such lasers would outshine our sun by several order of magnitudes if seen by a distant receiver. It can be shown that strong pulsed signals at nanosecond (or faster) intervals can be distinguishable from any known astrophysical sources.
Image: An MIT study proposes that laser technology on Earth could emit a beacon strong enough to attract attention from as far as 20,000 light years away. Credit: MIT.
The kind of system Clarke is talking about is not beyond our capabilities even now:
“This would be a challenging project but not an impossible one,” Clark says. “The kinds of lasers and telescopes that are being built today can produce a detectable signal, so that an astronomer could take one look at our star and immediately see something unusual about its spectrum. I don’t know if intelligent creatures around the sun would be their first guess, but it would certainly attract further attention.”
In terms of current capabilities, we can think about Clark’s 30-meter telescope in relation to plans for telescopes as huge as the 39-meter European Extremely Large Telescope, now under construction in Chile, or the likewise emerging 24-meter Giant Magellan Telescope. How and where to build such a laser is the same sort of issue now being analyzed by Breakthrough Starshot, which conceptualizes a series of small lightsail missions to nearby stars using laser beaming. Caveats include safety issues for both humans and spacecraft equipment. Clark suggests the far side of the Moon would be the ideal place for such an installation.
With METI (Messaging to Extraterrestrial Intelligence) continuing to be controversial, to say the least, whether or not we would ever choose to build an infrared laser as an interstellar beacon is up for question. But Clark’s analysis takes in the question of whether today’s technologies could detect such a signal if a civilization elsewhere put it into play and tried to communicate with us. As we’ve seen in other discussions of interstellar beacons, detection is highly problematic.
“With current survey methods and instruments, it is unlikely that we would actually be lucky enough to image a beacon flash, assuming that extraterrestrials exist and are making them,” Clark says. “However, as the infrared spectra of exoplanets are studied for traces of gases that indicate the viability of life, and as full-sky surveys attain greater coverage and become more rapid, we can be more certain that, if E.T. is phoning, we will detect it.”
We don’t know whether E.T. does astronomical surveys, but we know we do, and we are rapidly moving toward the study of small, rocky exoplanets through the spectra of their atmospheres. Thus Clark’s paper could be seen as a reminder to astronomers that an unusual signal could lurk within their infrared data, one that we should at least be aware of and prepared to analyze. A conversation between nearby stars at a data rate of a few hundred bits per second could eventually result.
The paper is Clark, “Optical Detection of Lasers with Near-term Technology at Interstellar Distances,” Astronomical Journal Vol. 867, No. 2 (5 November 2018). Abstract.
Bennu Coming into Focus
Following a week when we learned of the end of both Kepler and Dawn, let’s turn to a mission that is just coming into its own. The earliest images of target asteroid 101955 Bennu from OSIRIS-REx have been tightened by computer algorithm to heighten their resolution. The mission plan here is to examine the small object (approximately 500 meters in mean diameter) and return samples to Earth in 2023.
More than a few people have reacted to the similarity in shape between this asteroid, a carbonaceous (C-type) Earth-crossing object in the Apollo group of near-Earth asteroids, and 162173 Ryugu, now under active exploration by the Japanese Hayabusa2 mission. Here we’re looking at Bennu through the OSIRIS-REx PolyCam, one of three cameras aboard the spacecraft, from a distance of 330 kilometers. The image is a combination of eight images taken by PolyCam that have been combined to cancel out the asteroid’s rotation and produce a high-resolution result.
Of the comparison to Ryugu, Julia de León (Instituto de Astrofísica de Canarias – IAC) says this:
“The fact that the Japanese mission has reached its target a little ahead of us turns out to be extremely interesting, as we can now interpret our results and compare to the results obtained by another mission almost on real time.”
Image: This “super-resolution” view of asteroid Bennu was created using eight images obtained by NASA’s OSIRIS-REx spacecraft on Oct. 29, 2018 from a distance of about 330 km. The spacecraft was moving as it captured the images with the PolyCam camera, and Bennu rotated 1.2 degrees during the nearly one minute that elapsed between the first and the last snapshot. The team used a super-resolution algorithm to combine the eight images and produce a higher resolution view of the asteroid. Bennu occupies about 100 pixels and is oriented with its north pole at the top of the image. Date Taken: Oct. 29, 2018. Instrument Used: OCAMS (PolyCam). Credit: NASA/Goddard/University of Arizona.
The team from the IAC, which functions as part of the Image Processing Working Group (IPWG) for the OSIRIS-REx mission, is examining the early imagery from Bennu as an initial step in calibrations for comparison with later, higher-resolution images taken with color filters. In December, images from the spacecraft’s MapCam will begin coming in, putting those filters to work. The color maps thus generated will be used to break down the geographical distribution of silicates and other materials on the asteroid. And, of course, they will also play into the selection of a landing site from which a sample will be collected and returned to Earth.
OSIRIS-REx executed its third asteroid approach maneuver (AAM-3) on October 29, a set of thruster burns designed to slow the craft relative to Bennu from approximately 5.2 m/sec to .11 m/sec. The maneuver, verified by tracking data and telemetry, was designed to maximize the collection of high-resolution images as the spacecraft closes on the target. Another burn, the fourth in a series that began on October 1, will be executed on November 12, adjusting the craft’s trajectory for arrival at a position some 20 kilometers from Bennu on December 3.
And here’s another interesting image, a look at both Bennu and Jupiter, as seen by the OSIRIS-REx Polycam. The shot of Bennu was taken on October 22 of this year, with Bennu some 3,650 kilometers away, while the Jupiter image was captured on February 12, 2017 at a distance of 673 million kilometers. Notice the clear spherical shape of Jupiter as compared to the diamond-shaped Bennu, a shape predicted by ground-based radar observations.
Image: When these images were taken, Bennu was about five times closer to the Sun than Jupiter was, so the asteroid was receiving significantly more sunlight. If Bennu and Jupiter were equally reflective, the asteroid would appear about 25 times brighter in this image due to its proximity to the Sun. But Bennu’s surface is so dark (only reflecting about 3 to 4 percent of the incoming sunlight) that it appears darker than Jupiter despite being much closer to the Sun. Credit: NASA/Goddard/University of Arizona.
Carbonaceous C-type asteroids, as the image makes clear in this case, are low in albedo, presumably because of the large amount of carbon mixing with surface rocks and minerals.
If you’re tracking this mission closely, be aware of email updates that are available and check Twitter @OSIRISREx, Instagram or Facebook for more.
How many times is too many times to ask #AreWeThereYet on a single trip? Asking for a friend (who is now only a couple hundred kilometers from #asteroid Bennu)…
More on my whereabouts: https://t.co/rACre4nDe4 pic.twitter.com/tJaMcHw6qP
— NASA's OSIRIS-REx (@OSIRISREx) November 5, 2018
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