Asteroid Ryugu, We Can Almost Touch It / New Horizons Sees Ultima Thule

Surface of Ryugu photographed by Hayabusa2’s navigation camera on August 7 from an altitude of about 1 kilometer (0.6 mile). 10 meters or 32.8 feet is twice the size of a Volkswagen Beetle. JAXA, University Tokyo, Koichi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST

Seeing this close-up photo of the asteroid Ryugu really makes you appreciate the Earth. Just look at it. A beat-up pile of rocks and dust blasted mercilessly by the solar wind and cosmic rays 100 million miles from the sun. Gasp! No atmosphere either. The kilometer-wide asteroid currently has a visitor, the Japanese Hayabusa-2 spacecraft. It orbits about Ryugu taking pictures while preparing to gather its first sample of dust and pebbly grit in late October.

Here’s what we know about Ryugu right now:

  • It’s really dark! Ryugu reflects only 2% of the light it receives from the sun, absorbing the rest. Even the moon, which is as dark as an asphalt parking lot, reflects 12%.
  • Its day is 7.63 hours long.
  • It’s shaped like a top with an equatorial bulge.
  • It’s covered with boulders, the largest of which — 426 feet (130 meters) across — sits atop the south pole.
  • Its surface materials are all jumbled together in a diverse mineralogical mix.
  • It has a mass of 450 million tons. Assuming it’s rock, it’s not very dense, which could mean it’s porous and potentially a “rubble pile” asteroid.
Asteroid 162173 Ryugu photographed on June 26, 2018 from a distance of 12 miles (20 km) — a dark, stark, bouldery place. JAXA

Originally, the spacecraft was to gather several samples from different areas to collect a diversity of materials. But it’s since been discovered that Ryugu is diverse-all-over. To reduce the risk involved in sampling, the folks at JAXA (Japan Aerospace Exploration Agency) may make just one attempt near the asteroid’s equator.

At every sampling attempt, the Japanese probe will drop a target marker as an artificial landmark. JAXA

After a couple rehearsals in September and early October, the spacecraft will drop a reflective, weighted target marker on Ryugu’s surface to serve as an artificial landmark. The marker looks a little like a baby Sputnik with a reflective, gridded cloth exterior and short rods poking out. The spacecraft will shine a light on the marker, so the camera can fix on it. Then, as the probe gingerly descends to the asteroid’s surface, the landmark serves as a reference to detect any motion in the horizontal.  If there is any the craft will fire thrusters to land with zero motion in the horizontal, ie. without skidding.

Hayabusa-2 determines its vertical distance and speed from the asteroid by aiming a laser at the surface in a procedure called laser ranging.

After the sample is retrieved, the craft departs to a safe location in orbit. The samples are stored in a return capsule that will be come roaring through the atmosphere and land in 2020.

The photo on the left is a composite imagemade by adding 48 different exposures — each with an exposure time of just shy of 30 seconds — taken on Aug. 16, 2018. At right is a magnified view of the region in the yellow box, after subtraction of a background star field. Ultima Thule was 107 million miles (172 million km) from the New Horizons spacecraft and 4 billion miles (6.5 billion km) from the sun at the time. NASA/JHUAPL/SwRI

In other asteroid news, NASA’s New Horizon spacecraft has made its first detection in a photo of its new flyby target, the asteroid Ultima Thule. Mission team members were thrilled – if not a little surprised – that New Horizons’ telescopic Long Range Reconnaissance Imager (LORRI) was able to see the small, dim object while still more than 100 million miles away, and against a dense background of stars. Taken Aug. 16 and transmitted home through NASA’s Deep Space Network over the following days, the set of 48 images marked the team’s first attempt to find Ultima with the spacecraft’s own cameras.

While it doesn’t look like much yet, finding its target early will help mission controllers refine the spacecraft’s course to the remote asteroid, a member of the Kuiper Belt beyond the orbit of Neptune. The photo is also the most distant image from the sun ever taken. At the time the images were taken, the New Horizons spacecraft was 4 billion miles (6.5 billion km) from the sun.

New Horizons will make its closest approach to Ultima Thule (only the coolest-named asteroid ever) at 12:33 a.m. EST on Jan. 1, 2019.

7 Responses

    1. astrobob


      Man, you have a great memory. I forgot about those celestial diamonds. Thanks for the pleasant reminder you rough and rugged skywatcher.

      1. Richard Keen

        Well, you know what they say about long term memory. Now, about that movie I saw yesterday – or was it the day before?
        Speaking of memories, last night was the 43rd anniversary of the greatest astronomical thrill of my life. I stepped out in the fading evening twilight to check the sky, and noticed that Cygnus – the Northern Cross – looked very different, thereby discovering a “new star”, Nova Cygni 1975. Actually, if you count down on the IAU discovery circular
        you’ll see that I was the 45th recorded discoverer (Colorado had a longitudinal disadvantage). But no matter, even if I was the millionth, it was a thrill never to be forgotten.
        Keep looking up!

        1. astrobob

          Congratulations all over again on being one of the nova finders! I also remember that one back when I was going to school in at the U of I in Champaign. What a weird dimension it added to Cygnus.

          1. Richard Keen

            Bob, two questions…
            1. What was your major at U of I?
            2. How did you find out about Nova Cygni 1975? That IAU announcement was actually snail mailed several days after the discovery, and lots of folks didn’t get it until 4-5 days later. By then it had dimmed a magnitude or more.
            That event alone makes me really appreciate your quick diligence on posting new events up there, and why AstroBob is the first astro site I check every day (and again before dark).

          2. astrobob


            I majored in German with a teaching degree. I didn’t receive the IAU announcement via mail, but I was plugged into the university’s astronomy club. I can’t remember if I heard it there or if I spotted it completely on my own within a few days of outburst. I just remember noticing the distorted outline of the Northern Cross.

          3. astrobob

            Thank you for your nice comment about the blog, Richard. These days, I split my writing between the blog and the weekly observing pieces on Sky & Telescope.

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