Stargazing 04-07

The night sky in early April

The two asteroid missions — NASA’s OSIRIS-REx exploring Bennu and JAXA’s (Japan) Hayabusa 2 exploring Ryugu — have both found their asteroid subject has a lot more boulders on its surface than were planned for by mission designers. Both missions will be bringing samples of their asteroid back to Earth for analysis that requires instruments much too large to put on a spacecraft.

For sample collection, the technique that OSIRIS-REx was going to use required a hazard-free, smooth area at least 164 feet in diameter. Nothing like that exists on Bennu, so the team is creating a new plan that will require greater descent precision than the craft's design specifications. Fortunately, the spacecraft has been exceeding its design requirements, so the team is optimistic they’ll succeed. Necessity is definitely the mother of invention.

The Hayabusa 2 team is six months ahead of the OSIRIS-REx team and they have been able to maneuver their spacecraft for one touchdown-sample collection maneuver so far (along with deploying three small landers that floated down to Ryugu’s surface). Hayabusa’s sample collection technique has the spacecraft hovering just above the surface while it shoots a small bullet into the ground. Some of the material stirred up by the bullet’s impact will make it into a canister at the end of a meter-long pole extending from Hayabusa 2. Unfortunately, there is no sensor inside the canister to measure how much material is collected, so we’ll have to wait until the spacecraft returns to Earth to find out what is collected.

Hayabusa 2 was scheduled to fire a 5.5-pound projectile into Ryugu on Friday. The idea is to create a crater at least 30 feet wide and 3 feet deep and then take a sample from the middle of the crater. This will enable us to get material from the interior of Ryugu. The impact will also enable us to see how an asteroid will respond to a large impact if we have to nudge it in case we discover the asteroid is going to intercept the Earth.

Bennu will come very close to Earth between 2175 and 2196 and there’s just a 1 in 2700 chance of it hitting Earth. OSIRIS-REx’s study of Bennu will give us the information we need to more precisely predict Bennu’s future orbits. Scientists at NASA/JPL’s Center for Near-Earth Object Studies (CNEOS) figure that OSIRIS-REx will improve their trajectory projections of Bennu by a factor of 60 times. Ryugu has a much smaller chance of hitting Earth and doesn’t even make the top 75 objects of special interest in the CNEOS database.

Although both Bennu and Ryugu appear to be rubble-pile asteroids held together by gravity and have similar shapes (looking like spinning tops), Ryugu is much younger than Bennu and Ryugu appears to be much dryer than Bennu with much less hydrated minerals. A lot of Earth’s water is thought to have come from early watery-asteroid impacts, so Ryugu’s much drier composition is causing a re-examination of that thought and adjustment of the Earth formation models.

Eye on exoplanet

In exoplanet news, a team using the GRAVITY instrument on the European Southern Observatory’s Very Large Telescope (VLT) has obtained the first observation of an exoplanet using optical interferometry, which combines the light from an array of telescopes to create an image with the same resolution as a single telescope with a diameter of the array.

Each telescope in the VLT has an already impressive 8.2-meter mirror but when the four telescopes are combined through the interferometry technique, they act as a 100-meter telescope. Now, the resolution of such an instrument is what astronomers call “darn good." The GRAVITY instrument was developed specifically to probe the environment immediately outside the event horizon of the supermassive black hole at the center of our galaxy, the Milky Way (hence the name of the instrument). But its high resolution and spectroscopy capabilities was brought to bear on the young exoplanet HR8799e (yes, a name that ever so easily rolls off the tongue), which is about 129 light years from us and is in the Pegasus constellation.

Taking the spectrum of an exoplanet enables us to determine the composition of its atmosphere. The HR8799e spectrum gathered by GRAVITY is 10 times better than what’s been done before and it has enabled us to see the exoplanet’s atmosphere has a much higher than expected ratio of carbon monoxide to methane and clouds of iron and silicate dust. This suggests that HR8799e has enormous and violent storms with very strong vertical winds. That makes sense since the exoplanet is a super-Jupiter just 30 million years old.

In the night sky

Back in Bakersfield we can observe Mars now between the Pleiades and Taurus’ head in the west in the evening. Closer to the horizon will be a thin waxing crescent moon. The moon will be next to Mars and the Pleiades Monday evening and on April 12, the moon will be at first-quarter phase right next to Pollux at the top of Gemini. Full phase is on April 17.

A last note for stargazers: Tickets are on sale for the William M. Thomas Planetarium’s last show of the spring season, “Future of Space Exploration and the Journey to Mars,” on April 25. Purchase tickets at the BC Ticket Office, 1801 Panorama Drive, by calling 395-4326 or at vallitix.com.

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