The New Horizons probe has not yet gotten close to the asteroid Ultima Thule, but it is already transmitting data that confuses scientists. It turns out that the light curve of this object, located 6.4 billion km from Earth, is not similar to anything else in the solar system.

In a few days, the New Horizons probe will fly to Ultima Thule, a mysterious object on the very edge of the solar system. Since June last year, the device has been observing this distant asteroid and has already encountered the first riddle: the object turned out to be darker than scientists expected, and they cannot yet explain it, according to New Atlas.

One of the main methods for determining the shape of small objects in astronomy — asteroids or small planetoids — is to observe the light curve. In fact, it is a reflection of sunlight from the surface of an object, changing over time. For example, a perfectly round body will have a relatively flat light curve, since approximately equal amounts of light are reflected on each side.

However, the asteroid 2014 MU69, recently renamed Ultima Thule, surprised scientists. Previous observations have given rise to two hypotheses: either this is an object of irregular shape, or two objects located very close to each other. This means that it should have an uneven light curve, but this prediction was not confirmed. And it’s not that Ultima Thule suddenly turned out to be a round asteroid.

The New Horizons team did not detect any light curve at all.

“This is a real mystery,” Alan Stern, the principal investigator of the mission says. “I call it the first mystery of Ultima – why does it have such a tiny light curve that we can’t notice it? I suspected that the detailed images obtained during the convergence would pose new questions for us, but did not think that they would be like that any time soon.”

Scientists have several possible explanations, but not one that would satisfy everyone. For example, it is possible that a probe approaches an asteroid exactly along its axis of rotation. But this is unlikely. The second option: Ultima is surrounded by a cloud of dust, like a comet’s tail. But this is also doubtful, since it is too far from the Sun. Even more strange version: Ultima is surrounded by many tiny moons that have their own light curves, making it difficult to see the true one.

This is also possible, but makes the asteroid 2014 MU69 unlike any other body in the solar system.

While New Horizons is approaching a dark object in the solar system, the Parker probe is heading towards the Sun. In November, it approached the star at a record close distance of 24 million km and successfully withstood the load. It has 23 more such convergence maneuvers ahead.

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