We’re getting a few clues about the nature of planet migration in the early Solar System thanks to a class of objects being described as ‘blue binaries.’ Cold Classical Kuiper Belt Objects (CCKBOs) are generally reddish, but a population of widely separated binaries has now been identified that is thought to have originated in the inner edges of the Kuiper Belt.
The paper reporting on this work argues that these objects were pushed out a distance of over 4 AU to their present location among the CCKBOs as the result of gravitational interactions with Neptune billions of years ago, a movement induced by the migration of the planet from 20 to 30 AU. If so, we can draw some conclusions about that migration, and we’re reminded in the process of how rich the Kuiper Belt is in objects of different origins.
Led by Wes Fraser (Queen’s University, Belfast), the study used data drawn from the Gemini North instrument and the Canada-France-Hawaii Telescope, both on Mauna Kea, as part of a project called the Colors of the Outer Solar System Origins Survey. The team went to work on spectral data in a range of wavelengths from the ultraviolet to the optical and near-infrared. Its conclusion, reached by checking against models of Neptune’s migration, is that the blue binary pairs moved outward slowly enough that they were not disrupted into single objects.
Image: Artist’s conception of a loosely tethered binary planetoid pair like those studied by Fraser et al. in this work, which led to the conclusion that Neptune’s shepherding of them to the Kuiper Belt was gradual and gentle in nature. Credit: Gemini Observatory/AURA, artwork by Joy Pollard.
Let me quote from the paper re the team’s simulations:
The idea that the blue CCKBO binaries are contaminants that were pushed out into cold classical orbits during Neptune’s migration agrees well with the hypothesis that the blue–red bifurcation of the excited KBO colour distribution is a result of an object’s heliocentric formation distance. In our simulations, surviving binaries were pushed out by no more than 6 au, originating in the ?38–40 au range. Similar simulations suggest that the red-coloured, widely separated binary 2007 TY430, which now resides in the 3:2 MMR [mean motion resonance], plausibly originated at ?37–39 au, but could have originated even further out . This would require that the distance inside which blue binaries originated was only a handful of au inside the current inner edge of the cold classical region.
The Kuiper Belt contains a heterogeneous population indeed. Work by Alex Parker (University of Victoria, BC) and J.J. Kavelaars (Herzberg Institute of Astrophysics, Canada) tells us that the Cold Classical Kuiper Belt Objects are the only part of the Kuiper Belt population that formed in place. These objects share a reddish color, low inclinations and low eccentricities, a contrast to a population of dynamically excited objects that come in a range of colors.
Whereas this latter group is comprised of only about 10 percent binaries, the Cold Classical Kuiper Belt Objects exist as binary pairs about 30 percent of the time. The newly discovered blue binaries, though, distinguish themselves from both camps. In an email this morning, Dr. Fraser told me that while a few blue objects were previously known to exist in this region, his team had realized that the blue objects they were studying all came in binary pairs: “It was the discovery of blue+binary together that showed us we were looking at something special.”
Moreover, the binary nature of the objects as the products of Neptune’s ‘push out’ demands that they originally formed as multiple objects. From the paper again:
This push-out scenario would have the startling implication that virtually all planetesimals that formed in the region from which the blue binaries originated must either have formed as binaries or higher multiplicity systems, or attained high multiplicity before push-out occurred. This is required by the fact that all but one of the blue CCKBOs are found in binary pairs.
Thus we can see the blue binaries, originating at about 38 AU, as contaminants that in the paper’s language “…could provide a unique probe of the formative conditions in a region now nearly devoid of objects.” The paper explores various formation scenarios for these binaries that include pebble accretion and later binary production as well as binary formation from the collapse of a cloud of gas and solids that produces bound systems of two or more objects.
The paper is Fraser et al., “All planetesimals born near the Kuiper Belt formed as binaries,” published online by Nature Astronomy 4 April 2017 (abstract). The paper by Parker and Kavelaars cited above is “Destruction of binary minor planets during Neptune scattering,” Astrophysical Journal 722, L204–L208 (2010) (full text).
Our catalog of distant, highly energetic events continues to grow. On the Fast Radio Burst (FRB) front, we have the welcome news that the Molonglo radio telescope some 40 kilometers from Canberra, Australia has undergone extensive re-engineering, a project that is paying off with the detection of three new FRBs. The telescope’s collecting area of 18,000 square meters and an eight square degree field of view make it ideal for such work.
Image: Artist’s impression shows three bright red flashes depicting Fast Radio Bursts far beyond the Milky Way, appearing in the constellations Puppis and Hydra. Credit: James Josephides/Mike Dalley.
You’ll recall that Fast Radio Bursts are millisecond long, intense pulses that can appear out of nowhere with a luminosity a billion times greater than anything we have observed in the Milky Way. The phenomenon was noted for the first time a decade ago at the Parkes radio telescope in New South Wales. The sources remain enigmatic, but Manisha Caleb, a PhD candidate at Australian National University, has been developing software to examine the 1000 TB of data that is being produced daily at the Molonglo site. The new FRBs are the result.
“Conventional single dish radio telescopes have difficulty establishing that transmissions originate beyond the Earth’s atmosphere,” says Swinburne University’s Dr Chris Flynn.
But Molonglo (the Molonglo Observatory Synthesis Telescope, to give its full name, usually shortened to MOST) is a parabolic, cylindrical antenna consisting of 88 bays, each of these made up of four identical modules, to produce 352 independent antennae. The upgrade to the Molonglo instrument is known as UTMOST. The researchers used the array in a 180-day survey of the Southern sky, carrying out up to 100 hours of follow-up for each FRB, though no repeating bursts were seen. A repeating burst at UTMOST, or an FRB simultaneously detected at Parkes and UTMOST, would allow a localization of a few arcseconds.
From the paper (note that ” is the symbol for arcseconds):
In this paper we present the first interferometric detections of FRBs, found during 180 days on sky at UTMOST. The events are beyond the ≈ 104 km near-field limit of the telescope, ruling out local (terrestrial) sources of interference as a possible origin. We demonstrate with pulsars that a repeating FRB seen at UTMOST has the potential to be localised to ≈ 15″ diameter error circle, an exciting prospect for identifying the host.
Image: View of the MOST at the end of the East arm looking West. Two arms, each 800 meters long, together have a collecting area of circa 18,000 square meters. MOST is the largest radio telescope in the Southern hemisphere. Credit: Swinburne University/UTMOST.
The recent discoveries point to a new ability to locate FRBs in the sky, allowing us to link them to specific galaxies, a feat that has been accomplished only once so far (see Pinpointing a Fast Radio Burst). The paper is Caleb et al., “The first interferometric detections of Fast Radio Bursts,” accepted at Monthly Notices of the Royal Astronomical Society (preprint). For more, see this UTMOST news release.
With my own memories of the July 4, 1997 landing of Mars Pathfinder at Chryse Planitia as fresh as yesterday, it’s hard to believe that we are looking at the 20th anniversary of rover operations on the planet. But as the Curiosity rover continues its travels and we look toward the Mars 2020 rover mission, we’re also taking a much longer look ahead at the worlds where life may be more likely to be found, the icy moons of Jupiter and Saturn.
Ponder this: Testing at the Jet Propulsion Laboratory is showing that ice grains in conditions like we will encounter on places like Enceladus or Europa can behave like sand dunes. That means fine grains that could stall an improperly designed rover, leading NASA engineers to begin rethinking designs harking back to the early days of Moon exploration, lightweight commercial wheels attached to a flexible chassis, a system that has worked for a variety of missions but will need adjustment for future work. The rovers that use these systems will, in the case of moons like Europa, need serious attention to radiation hardening.
Image: Artist’s concept of Europa’s frozen surface. Credit: JPL-Caltech.
The project looking into extreme environments for these next generation rovers is called the Ocean Worlds Mobility and Sensing study, which is developing prototypes for sample acquisition on icy moons. Working tricky environments like Enceladus means coping with fissures that blow jets of material out into space. And Europa’s challenge goes far beyond Jupiter’s cascading radiation given the need to get through surface ice to sample the subsurface ocean. On Titan, we prepare for a possibly mushy ethane-rich surface.
“In the future, we want to answer the question of whether there’s life on the moons of the outer planets — on Europa, Enceladus and Titan,” says Tom Cwik, who leads JPL’s Space Technology Program. “We’re working with NASA Headquarters to identify the specific systems we need to build now, so that in 10 or 15 years, they could be ready for a spacecraft.”
The Europa work is particularly interesting given the question of astrobiology in the Europan ocean. The biggest problem for designers right now is that we have no certainty about the thickness of the surface ice, which could conceivably extend as deep as 20 kilometers. Richard Greenberg has argued in Unmasking Europa (Copernicus 2008) that the evidence of surface melt-through of Europan ice points to ice as thin as five kilometers. Whatever the case, so-called ‘melt probe’ designs are being scaled up for the challenge.
The JPL work on melt probes is led by Brian Wilcox, who has concluded that the thickness of Europan ice, in comparison with the Earth ices that conventional melt probes have coped with, demands an emphasis on heat efficiency. Wilcox is examining a vacuum-insulated capsule that uses a heat source like plutonium to keep its energy as it sinks into the ice. At one end, a rotating sawblade turns and cuts ever deeper, while pushing ice chips into the body of the probe, where they are melted and pumped out behind it.
The idea is that the water would be sampled in the midst of this process, with some being returned to the surface lander through pneumatic tubing. There it would be checked for biosignatures. And given concerns about possible contamination by Earthly life, Wilcox would heat the probe to almost 500° C during the cruise phase of the flight, thus killing off any residual organisms that may be hitching a ride from Earth.
“We think there are glacier-like ice flows deep within Europa’s frozen crust,” Wilcox said. “Those flows churn up material from the ocean down below. As this probe tunnels into the crust, it could be sampling waters that may contain biosignatures, if any exist.”
This JPL news release offers more, including work on a new generation of robotic arms that will out-reach our Mars rovers, which have never extended beyond about 2.5 meters from the base unit. JPL is looking at a robotic arm with a 10 meter extension, and is also considering a projectile launcher that can fire a sampling mechanism to distances of 50 meters. Having obtained the sample, the device would be reeled in by a tether.
These technologies are designed to be used along with an ice-gripping claw which could have a coring drill attached to it for taking surface samples at locations of interest. The drill would be able to reach about 20 centimeters below the surface ice. The ice claw itself would be deployed from a boom arm and would anchor itself with heated prongs that melt into the ice to secure the unit. It would then penetrate the ice with its drill bit to collect the needed sample.
Image: A robotic claw, one of several innovative tools developed at JPL for exploring icy, ocean worlds like Europa. Credit: NASA/JPL-Caltech.
The Ocean Worlds Mobility and Sensing site is sparse at the moment but it’s one you might want to keep an eye on as the effort continues. NASA is considering a second phase of the study that would be tapped as we work out the overall design of any icy moons lander.
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to others, I'm probably not going to run it.
