By Kim Malville
January 1, 4:33 am MST: The first radio signal from the New Horizons spacecraft when it flies past Ultima Thule should arrive. The encounter occurred six hours earlier but it takes light and radio waves those six hours to cross the 4 billion miles separating is from the Earth.

January 3-4: The maximum of the Quandrantid meteor shower takes place this night. The radiant of the meteors will be close to the northern horizon.

January 6: Partial solar eclipse in east Asia and far west Alaska.

January 12: Close approach (as seen from the earth) of the moon and Mars.

January 20: Total lunar eclipse in Crestone. This is the night of a full moon, which rises just as the sun sets. THe first hint that the moon is entering the shadow of the earth will be at 8:10pm MST, and the moon will clearly be entering the shadow on 8:34pm MST. The moon will fully enter the shadow of the earth on 9:41pm MST and will remain eclipse for 63 minutes. This may the kind of eclipse that has frightened generations for millennia. Look for the blood red moon as it gets colored by millions of sunsets around the earth.

January 30: The moon and Jupiter will be close to each other in the sky.

New Horizons reaches Ultima Thule

After its spectacular fly-by of Pluto in July 2015, the New Horizons space craft has been moving at 36,000 miles per hour to the most distant object ever explored in the solar system, now known as Ultima Thule. The space craft will fly past this chunk of rock and ice at 12:33 EST on January 1 and then beam back what is photographed and measured. As I finish writing this column on December 26, New Horizons is some 4 million miles away and closing in on its target by 864,000 miles per day. When you read this column you will know whether or not New Horizons has been successful. IN any case, the full story will emerge slowly. Throughout January and the succeeding 19 months, the data will continue to flow to the Earth. It has been a long journey for New Horizons, which was launched in January 2006.

This will be a truly extraordinary event on New Year’s day. Ultima, which is officially known as 2014 MU69, has been in a deep freeze since the birth of the solar system 4.6 billion years ago. This will be the most distant and most pristine object ever explored by human kind. This tiny rock is some 20 miles across and lies at a distance of 4 billion miles. Observing it from the Earth is comparable to viewing a grain of sand from a distance of 250 miles!

New Horizons will fly past Ultima at a distance of 2200 miles, about three times closer than it got to Pluto. During the first two weeks of December, the New Horizons took hundreds of images of Ultima Thule, enabling team scientists to search for evidence of satellites or dust things that could pose a hazard to the spacecraft. At its speed, an impact with a millimeter-sized ice pellet could end the mission. Nothing threatening was found along its flight path and the final trajectory was established on December 18.

One puzzle that emerged from inspection of those images is that there is no evidence of brightness variation as it rotates. Measurements from Earth show it to be very elongated or consisting of two closely orbiting objects. It should be roratings, yet there is no change in its brightness over time. Team members have come up with several possible explanations. For example, maybe Ultima’s pole of rotation just happened to be pointed directly at New Horizons, minimizing the brightness variations seen by the spacecraft.

It’s also possible that Ultima is surrounded by a light-blocking cloud of dust like the coma around a comet’s nucleus, which only appears when the comet gets close to the sun. But an energy source would be required to generate such a feature, and it’s unclear what that source would be. But, this is a worry. Such a cloud of dust would mean the space craft could not detect the actual surface of the object. An even more bizarre scenario is one in which Ultima is surrounded by many tiny, tumbling moons, each rotating at a different rate, which might produce a hazard for the space craft.

Ultima is too small and too distant for the Hubble Space Telescope to measure its size or shape. The only other means is to measure the size and shape of the shadow it cast on the earth when it passes in front of a star. This is an eclipse of a star, vastly more difficult to detect than the total eclipse of the sun. The technique is to monitor the brightness of the star and look for a drop of brightness.

On 3 June 2017, a team of astronomers tried to detect its shadow from South Africa. None of their telescopes observed the shadow. Either Ultima might be smaller than expected or the telescopes were in the wrong location. The Hubble Space Telescope was called into action, and Ultima’s orbit was determined more accurately. The next attempt was successful. On July 17, the team was sent to southern Argentina to set up a picket fence of 24 telescopes with an average spacing of 2.8 miles. The figure shows the locations of the telescopes strung along the coast near the city of Comodora Ricadiva, some 1000 miles south of Buenos Aires. Five os those telescopes detected the shadow, mapping out its exact shape. Because a star is a point source, its shadow on the earth is an exact replica of Ultima, which we know now consists of two roughly spherical blobs some 12 and 11 miles across. Finally the experiment was repeated in August of this year in Senegal adding more information. I’m pleased to say that an undergraduate student, whom I’ve been advising in our department at the University of Colorado, has had the extraordinary opportunity to be involved on all three of these occultation experiments.