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Star window provides rare view of solar system’s distant fringe


Blinking star reveals the target of New Horizons space probe, 6.5 billion km away


An artist’s rendition of Kuiper Belt Object MU69, which New Horizons will visit in January 2019.
An artist’s rendition of Kuiper Belt Object MU69, which New Horizons will visit in January 2019.
NASA, ESA, SWRI, JHU/APL, AND THE NEW HORIZONS KBO SEARCH TEAM

Astronomers in Argentina have just caught a rare glimpse of an object 6.5 billion kilometres away, in the very outer reaches of the solar system, when its orbit took it between Earth and a background star.

Kuiper belt object 2014 MU69 passing in front of a background star in the constellation Sagittarius.
Kuiper belt object 2014 MU69 passing in front of a background star in the constellation Sagittarius.
NASA / JHUAPL / SwRI / Emily Lakdawalla

Scientists associated with the New Horizons space probe, which after taking a close look at Pluto in 2015 will rendezvous with the object – known as MU69 – around New Years’ Eve 2018, have been watching closely in recent weeks as MU69 has passed in front of three background stars.

These events, known as occultations, can provide vital information about the object, which is much too small and distant to see directly. While predicted occultations on June 3 and July 10 delivered some useful information, they did not produce the hoped-for observations. On July 17, however, the stars (and smaller heavenly bodies) aligned to reveal a tell-tale momentary stellar wink.

MU69 sits in the Kuiper belt, a broad disc of small floating bodies out beyond Neptune at distances 30 to 50 times further from the Sun than the Earth. In some ways the Kuiper belt mirrors the asteroid belt that occupies a ring between the orbits of Mars and Jupiter, though Kuiper belt objects are generally much icier than the rocky asteroids closer to the Sun.

Very little is known about MU69: it was only discovered in 2014, when astronomers pointed the Hubble Space Telescope at the Kuiper belt to look for something interesting beyond Pluto that New Horizons might be able to manoeuvre itself towards, and because it is so tiny and distant it is hard to get a good look.

Studying the images of the occultation will give the New Horizons time vital data about the size and other properties of MU69, to ensure that everything goes smoothly when the space probe wakes up late in 2018 to take a look at the most distant object ever explored by spacecraft.

It will be some weeks before the data from the occultations is analysed, according to the NASA press release.

Michael Lucy is features editor of Cosmos.
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