New Outcomes Probe the Origin of “Final Thule”

March 19, 2019 - Comment

As observations trickle in from NASA’s New Horizons spacecraft, mission scientists have new insights on how their two-lobed goal shaped within the Kuiper Belt. It has been 2½ months since NASA’s piano-size New Horizons zipped previous a tiny goal within the Kuiper Belt within the first hours of New Yr’s Day. That physique, designated 2014


As observations trickle in from NASA’s New Horizons spacecraft, mission scientists have new insights on how their two-lobed goal shaped within the Kuiper Belt.

It has been 2½ months since NASA’s piano-size New Horizons zipped previous a tiny goal within the Kuiper Belt within the first hours of New Yr’s Day. That physique, designated 2014 MU69 and nicknamed “Ultima Thule” by mission scientists, wasn’t even found till 8½ yr after the spacecraft’s launch. For the reason that flyby, sufficient observations have trickled again to Earth to begin to piece collectively this object’s outstanding story — and this week these first chapters are being offered on the annual Lunar and Planetary Science Convention.

Ultima Thule

New Horizons captured this picture of 2014 MU69 from a distance of simply four,200 miles (6,700 km). It resolves particulars as small as 440 ft (135 meters) per pixel. The bigger lobe (dubbed “Ultima”) is about 12 miles (19 km) throughout; smaller “Thule” is 8½ miles (14 km) throughout. Be aware the distinct melancholy on Thule and the small craters alongside the highest limbs of each lobes.
NASA / JHU-APL / SWRI

In a way, the 40 flyby-related displays at LPSC characterize the science group’s first “victory lap” with their friends. As principal investigator Alan Stern (Southwest Analysis Institute) factors out in his most up-to-date weblog for S&T.com, “Each deliberate remark, by each one of many scientific devices aboard New Horizons, carried out in line with plan.”

Most intriguing are the outcomes that element 2014 MU69’s floor geology and composition — and what these reveal about this curious object’s origin. This physique has a dynamically “chilly” orbit: Its low inclination and eccentricity recommend that nothing has perturbed its movement considerably. So, crucially, the spacecraft had the nice fortune to look at a pristine relic that shaped on the outer fringe of the photo voltaic nebula 4½ billion years in the past.

A Flattened Snowman

Early returns from New Horizons revealed an object 35 km (21 miles) lengthy with two like-sized lobes that resembled a yard snowman. However as extra pictures reached Earth, it turned clear that each lobes have a flattened form, with the bigger one (dubbed “Ultima”) extra so than considerably smaller “Thule.”

The 2 lobes have a lumpy uneven texture that investigator Kirby Runyon (additionally at SwRI) likens to spherical loaves of “monkey bread.” Just a few small pits seem across the edges, however general the floor is not closely cratered. Actually, a big melancholy on Thule that the group has dubbed Maryland could be the one giant crater in view.

Total each lobes are darkish, 7% reflective on common with a number of brighter spots right here and there. (It is a shut match to the reflectivity of the Moon.) The brighter spots may mark the places of degraded impacts, however the “high-Solar” illumination makes it troublesome to know in the event that they’re depressions or one thing else.

A lot of the group’s consideration has centered on the slim “neck” the place the 2 lobes be part of. The proof recommend a delicate merger — there aren’t any “splat” deposits or stress fractures, for instance — and the contact is girded by a skinny “collar” that is each brighter and fewer pink than elsewhere. Up to now, investigators can solely guess how and when it received there.

Colour Cues

Extra than simply being darkish, the floor of 2014 MU69 is strongly pink. Because the plot at proper reveals, it is among the reddest materials within the outer photo voltaic system. However, as Silvia Protopapa (SwRI) notes, it is also an in depth match to the pink hue of different “chilly, classical” Kuiper Belt objects which were noticed from Earth.

Solar-system color comparison

Though 2014 MU69 could be very strongly pink, its colour is an effective match to that of different objects within the “chilly, classical” Kuiper Belt — objects with orbits which can be roughly round and have low inclination, suggesting they haven’t been strongly perturbed because the photo voltaic system’s formation.
NASA / JHU-APL / SwRI

The LEISA spectrometer aboard New Horizons scanned the floor repeatedly because the spacecraft swept by. The ensuing spectra not solely verify the strongly pink floor coloration but additionally reveal three distinct dips at near-infrared wavelengths. These at 1.5 and a couple of.zero microns are as a consequence of water ice, Protopapa reviews, and the third at 2.27 microns reveals the presence of methanol (CH3OH). This easy natural compound, usually noticed in outgassing comets, types when methane (CH4) is oxidized.

All this matches properly in an general image: Kuiper Belt objects ought to have contained ample methane and water ice once they shaped, and over time area radiation and ultraviolet photons from the distant Solar would have transformed these into extra advanced hydrocarbons, often known as tholins, with distinctly darkish, reddish hues. How a lot water and methane may lie deeper down is unknown: For the reason that two lobes are involved, slightly than orbiting each other, there is no approach to decide their density and thus achieve clues to their general composition.

Ideally, a tiny moonlet would flip up in one of many pictures nonetheless saved aboard New Horizons. That discovery would shortly present a density estimate for 2014 MU69. Stern factors out that it’ll take till August or September of 2020 to obtain all of the flyby observations. These probably will present many extra discoveries and surprises.



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