NASA’s New Year’s Day Kuiper Belt encounter with the solar system’s history

New Year’s day 2019 will provide a fascinating juxtaposition between the future and the past for NASA’s New Horizons probe as it prepares for an encounter with a primordial object that likely formed at the very dawn of the solar system. The encounter will be the most distant exploration of an object in the solar system to date.

Seconds after the clock strikes midnight at Johns Hopkins University Applied Physics Laboratory (APL), the New Horizons probe -which APL control for NASA-will pass MU69, a 35-kilometre-wide object some 6.6 billion kilometres away, in a far-off region of the solar system called the Kuiper belt, at a speed of 14 km/s.

The reason that this is so exciting is that unlike any other object thus yet glimpsed by the probe, MU69 - nicknamed “Ultima Thule” or “ land beyond the known world”- has remained virtually unchanged since the cloud of dust and gas that formed our solar system collapsed 4.6 billion years ago.

The probe will take a series of images of MU69 whilst simultaneously collecting other data about the object. Thus, observations of the object should allow astronomers to stare back into our solar system’s history.

Alan Stern, the mission’s principal investigator, explains the significance of a visit to MU69: “No one’s ever been to this kind of object, so pristine and primordial.”

An artist’s depiction of MU69, also known as Ultima Thule, a solar system body about to be visited by the New Horizons spacecraft (NASA. John Hopkins. Parker)

Dr Kelsi Singer, a scientist working on the mission details the kind of data expected to be collected: “About one day out we’ll turn on all our instruments.

“We’ll take black and white images; we’ll take colour images. And we’ll take compositional information… This is just such a new object because we’ve never been to an object like this before. It’s hard to predict but I’m ready to be surprised by what we find.”

The Kuiper Belt: a window to the past

The Kuiper Belt, where MU69 is located, is comprised of icy-bodies- referred to as Kuiper Belt objects (KBOs) or trans-Neptunian objects (TNOs)- lying beyond the orbit of Neptune. These icy-bodies can be loosely defined as the remnants of the early history of the solar system.

Until the 1990s, researchers were unaware whether the Kuiper belt- which may actually be better described as a doughnut- actually existed at all. The objects were difficult to observe because of their relative lack of size and their dimness. Since this time, however, astronomers have successfully detected thousands of objects in the region.

The first detection of MU69 with the highest resolution of New Horizons telescope, taken on Christmas Eve (NASA. John Hopkins)

The Hubble space telescope was able to identify five suitable candidates for a visit from New Horizons with HU69 selected as it could be reached quickest. Happily, this plan also provides a rather poetic encounter on the first day of 2019.

The APL will be examining the surface of Ultima Thule for the number of craters left by impact by other objects. Pluto-a fellow Kuiper Belt occupant-was marked with far-less impact craters than astronomers expected. Given the belt’s relative calm conditions, if MU69 reflects the surface of Pluto it gives researchers a good idea about the size of objects that occupied the early solar system. It will also give astronomers a fair idea of the disturbances caused by the planets in the solar system moving into their current orbits.

The images of Pluto’s surface taken by New Horizons revealed surprisingly few impact craters (NASA. John Hopkins)

Researchers will also be looking to catch a glimpse into one of these craters in order to ascertain MU69’s composition. They assume that Ultima Thule is comprised mostly of water-ice, as are most bodies in the outer solar system, but as with most Kuiper Belt objects, it has a reddish hue, the origins of which researchers are currently unsure of.

The surface of MU69 may well indicate the mechanism by which planets form. A new theory, growing in popularity amongst astronomers, suggest that turbulence clumps particles together in a cloud which then collapses under gravity, contrary to previous theories which suggested the accretion of material as objects gas through gas and dust clouds. If this new theory is true, these particles should be visible on the surface of MU69.

Wesley Fraser, an astronomer at Queen’s University Belfast, says: “If it did evolve from a cloud of particles, we should see those actual particles on the surface of MU69.

“It should be a clump of pebbles stuck together.”

The challenges facing New Horizons

Artist’s impression of the New Horizons Probe (NASA)

The Ultima Thule flyby is similar to New horizon’s activities around Pluto but is likely to be more of a challenge to the operating team.

For a start, the probe’s nuclear power source is now waning. Secondly, this flyby is further away than Pluto, this means that as a signal from APL now takes six hours to travel to New Horizons, the operation must be far more carefully choreographed. Difficult to do under normal circumstances, but the APL team is now much smaller than it was and has had far less time to prepare for this mission than it did for the Pluto flyby.

Another potential hindrance is that less is known about the orbit of MU69 than that of Pluto. Whilst Pluto’s orbit had been charted extensively before New Horizons made its flyby of the dwarf planet, Ultima Thule was discovered just 4 years ago and its trajectory is somewhat unknown.

To prepare for any surprises that could derail the mission New Horizons’ telescope scoured the area around MU69 last month searching for any small objects which may impede or damage the probe. And up until just yesterday (30/12/18), the APL team were using the telescope to observe MU69’s position so that the onboard camera can be properly refined to capture the best possible images of Ultima.

Happily, as APL is an outside contractor, they are not subject to the federal shutdown which has affected NASA and other government agencies.

New Horizons’ certain uncertainties

Until the first images of Ultima Thule are received by the APL team at John Hopkins late on New Years Day, researchers are unsure of what the data collected will actually tell them.

In fact, they aren’t even certain that MU69 is a single object. Its oblong shape could indicate it is a small binary unit, something that is believed to be fairly common in the Kuiper Belt, accounting for approximately a third of objects found there.

As mentioned above, early observations have revealed Ultima’s reddish hue, a common characteristic of Kuiper Belt objects, this commonality makes it an ideal choice for study as researchers are looking for an object to examine which will tell them about the Kuiper Belt in general.

And this will be just the first of many Kuiper Belt objects examined by New Horizons. One thing that is certain is that many mysteries about the formation of the solar system and our planetary neighbours will be answered in 2019.