Feb 12

What’s Up in the Sky

What’s Up in the Sky – February, 2019

Ultima Thule – A Blast From the Past

Late last year, an object with a very interesting name was in the news. That was Ultima Thule, the latest discovery made by the New Horizons spacecraft. Go to https://apod.nasa.gov/apod/astropix.html, click on “Archive” and look at the photo from January 29.

At that time not much was known about this object other than it had a weird name. In order to find out what we have discovered so far I turned to a reliable source, Dr. Harold Reitsema, a project scientist on NASA missions who worked on New Horizons. Dr. Reitsema is also a member of the Shoreline Amateur Astronomical Association, and Holland resident and agreed to an interview for this story.

“Thule” refers to the edge of the known world, and is a term that has been around for about a thousand years. “Ultima” simply reinforces that idea and is appropriate because it is the most distant object in the solar system to be visited by a spacecraft and that is where New Horizons is. It is an informal name chosen from a list of submissions to an internet poll. Currently, the real name is 2014 MU69 (which is kind of “nerdy” in Dr. Reitsema’s view) but even that is only temporary until the International Astronomical Union assigns a permanent name that follows current protocol.

Ultima Thule resides in the Kuiper belt, a region of the solar system that extends about 10 AUs beyond Pluto (an AU, or astronomical unit, is the average distance from the Earth to the Sun) and contains over a million asteroid-like objects ten kilometers or larger in diameter. It was discovered in 2014, eight years after New Horizons was launched. It took a massive effort by New Horizons team members using the Hubble Space Telescope, to pinpoint its location.

Based on these observations, New Horizons was able to make small corrections in its trajectory that allowed it to pass a little over three thousand kilometers (slightly less than two thousand miles) of its target. That’s like sinking a three pointer from over two hundred eighty miles.

So why Ultima Thule? What could we possibly learn from a tiny object so far away? Dr. Reitsema explained that the very early stages of the formation of the solar system are difficult to study due to a lack of data from samples dating back 4.5 billion years. Planets, their moons, and asteroids have all undergone changes since the solar system first formed. The craters on the Moon are an example. Even Pluto suffered a great collision that formed its moon, Charon. Dr. Reitsema explained that we wanted to “look at a very pristine thing that looks like it did when it formed”. So this object, undisturbed since its formation, is going to look like what “small things that got together and made bigger planets looked like originally”.

There is still more to learn about Ultima Thule and much evidence is forthcoming from pictures that have yet to be downloaded from the spacecraft. At the time of my interview, there was very little evidence of impact craters on its surface, but as you can see from the picture mentioned above, we continue to learn much each week as additional images arrive. That picture alone explains why people like Dr. Reitsema devote their careers to studying what’s up in the sky.

This month in history:
Feb. 1: Shuttle Columbia breaks apart during reentry killing all 7 astronauts – 2003
Feb. 7: First untethered spacewalk made by Bruce McCandless – 1984
Feb. 14: Voyager 1 looks back to take photo of solar system – 1990
Feb. 18: Pluto discovered – 1930
Feb. 20: John Glenn is first American to orbit Earth – 1962
Feb. 28: Charles Bassett and Elliot See, Gemini IX crew, die in plane crash – 1966