In the first few hours of 2019, NASA’s New Horizons spacecraft flew past a small distant and icy world situated in the enigmatic Kuiper belt 1.5 million kilometres beyond Pluto, nicknamed Ultima Thule, inaugurating an era of exploration of a primordial region in space.
Launched in 2006, New Horizons registered its closest approach to Ultima Thule at just 3,500 kilometres from the object. At that time, Ultima Thule was at a distance of almost 6.5 billion km from the Sun, making this the most distant planetary flyby that has yet been attempted, and the first time that a solar system object of this type has been seen close-up.
The most distant and ancient object in the solar system so far, Ultima orbits the Sun in a region called the Kuiper Belt, which comprises a collection of debris and dwarf planets. With the discernible shape of a snowman, and named after the two lobes of its bowling-pin structure, Ultima Thule holds the key to understanding the origins of the solar system 4.6 billion years ago.
The event recorded the farthest ever exploration of a solar system object, breaking the previous record, also set by New Horizons, during 2015’s flyby of the dwarf planet Pluto. Within 10 hours of its closest approach to Ultima, healthy signals from the probe confirmed reception of data, less than 1% of which has been downlinked to Earth so far. The probe will continue downloading images and other data in the days and months ahead, completing the return of all science data over the next 20 months.
What we know about Ultima Thule so far
According to the Washington Post, Ultima Thule is a “rocky relic from the solar system’s infancy whose name means ‘beyond the borders of the known world'”. The new images taken from a distance of 27,000 km on approach revealed the object as a “contact binary”, that is, it is composed of two bodies that have gravitated toward each other until they touched. End to end, the oblong object measures 19 miles (31 kilometres). The team has dubbed the larger sphere “Ultima” (12 miles/19 kilometres across), and the smaller sphere “Thule” (9 miles/14 kilometres across).
They also showed that the object is spinning end over end like a propeller with the axis pointing towards the probe. The mission team thinks that the two spheres were joined at the time of its origin, at the speed of two cars colliding in a fender-bender, in a volume ratio of 3:1.
The best of the pictures shared by the team on Wednesday were taken while the probe was still 28,000 km from Ultima. In these images, surface features higher than 140 metres are discernible. Those captured at the moment of closest approach are expected in February and will have a resolution of about 35 metres per pixel.
Flyby data from NASA’s spacecraft further shows how dark the Kuiper Belt object is. It reflects 6-13% of the sunlight its receives, which likens the surface composition to potting soil, according to Cathy Olkin, the mission’s deputy project scientist from the Southwest Research Institute (SwRI).
The team was able to definitely say that Ultima Thule is red based on a rough colour received from Hubble data, and with the current proof which allows for a more composite theory. The reddish tinge owes itself to the irradiation of exotic ices, implying that Ultima’s surface has been “burnt” over billions of years by high-energy cosmic rays and X-rays in space.
Principal investigator Alan Stern commented on the scale of the object, saying, “[Ultima’s] only really the size of something like Washington DC, and it’s about as reflective as garden variety dirt, and it’s illuminated by a Sun that’s 1,900 times fainter than it is outside on a sunny day here on the Earth. We were basically chasing it down in the dark at 32,000 mph (51,000 km/h) and all that had to happen just right.”
Significance of the project
Members of the Kuiper Belt and their frigid state are believed to hold clues to how planets in the solar system originated 4.6 billion years ago. But Ultima is unique and because of its distance from the sun, which keeps the temperature 30-40 degrees above absolute zero — the coldest that atoms and molecules can possibly get. Chemical reactions are thus absent, keeping it in a deep freeze which means that Ultima’s original state is probably preserved.
The nature of Ultima’s environment is also suspected to be quite inert, further nullifying chemical reactions. The object is also small and therefore, does not have the “geological engine” of larger bodies to rework its composition.
Stern believes that none of the objects that NASA has flown by, landed on, or orbited so far, can tell us about the origins of the universe because “they’re either large and evolve, or they are warm”. “This flyby is a historic achievement,” he said, adding, “Never before has any spacecraft team tracked down such a small body at such high speed so far away in the abyss of space. New Horizons has set a new bar for state-of-the-art spacecraft navigation.”
Mumbai-based space engineer Shyam Bhaskaran played a key role in navigating the New Horizons spacecraft to its object with accuracy and desired proximity, which enabled the historic photography of Ultima Thule this week.
Working out of NASA’s Jet Propulsion Laboratory, Bhaskaran told the Times of India that this mission was comparatively easier than the one to Pluto because of the absence of space debris and other objects on its way.
Ecstatic finish to a nail-biting journey
The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, designed, built and now operates the New Horizons spacecraft, and manages the mission for NASA’s Science Mission Directorate. The Southwest Research Institute, based in San Antonio, leads the science team, payload operations and encounter science planning. New Horizons is part of the New Frontiers Programme managed by NASA.
NASA Administrator Jim Bridenstine congratulated the entire team, saying, “In addition to being the first to explore Pluto, today New Horizons flew by the most distant object ever visited by a spacecraft and became the first to directly explore an object that holds remnants from the birth of our solar system.”
“Reaching Ultima Thule from 4 billion miles away is an incredible achievement. This is exploration at its finest,” said Adam L. Hamilton, president and CEO of the Southwest Research Institute in San Antonio. “Kudos to the science team and mission partners for starting the textbooks on Pluto and the Kuiper Belt. We’re looking forward to seeing the next chapter.”
Prarthana Mitra is a staff writer at Qrius
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