10/04/2022 – Ephemeris – DART does its job, now we wait and watch.

This is Ephemeris for Tuesday, October 4th. Today the Sun will be up for 11 hours and 33 minutes, setting at 7:17, and it will rise tomorrow at 7:45. The Moon, 2 days past first quarter, will set at 2:14 tomorrow morning.

Last week Monday night NASA’s DART spacecraft successfully smashed into the tiny asteroid Dimorphos, which was slowly orbiting an asteroid named Didymos five times its size, and nearly a half mile in size. Dimorphos is too small and too close to Didymos to be seen in optical telescopes. Even the DART spacecraft’s telescope could only spot it in the last hour before the collision. Astronomers have found that they can see asteroid shapes and moonlets by radar. One technique was to send out radar pulses out from the Arecibo Observatory in Puerto Rico and receive them back with the Green Bank Telescope in West Virginia. Now that Arecibo has been destroyed, astronomers transmit from Goldstone, California.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

Dimorphos collision from as seen from Hubble and JWST. The colors aren’t true. Credit: NASA, ESA, CSA, Jian-Yang Li, Cristina Thomas, Ian Wong, Joseph DePasquale, Alyssa Pagan. From CNET web site.

10/02/2022 – Ephemeris Extra – NASA goes on the offensive

DART images of both Didymos, the big one, and Dimorphos, on approach. Credit NASA / JHAPL

This is a slightly revised version of my article in the Stellar Sentinel, the newsletter of the Grand Traverse Astronomical Society. Educators may receive a free PDF copy of this monthly publication via email, which covers astronomical topics and events visible from Northwest Lower Michigan. Send your request, stating your affiliation, to info@gtastro.org.

The score is: Asteroids-billions, NASA-1. It’s a bit unfair, since asteroids have been hitting the Earth for 4.567 billion years or so, and NASA has been around for 64 years before DART spacecraft collided with the asteroid Dimorphos. Hey, this was their first attempt at a small asteroid. As far as the 21st century destructive asteroid score is 1 to NASA’s 1, as far as I know.
That strike was in Chelyabinsk, Russia. That was February 15, 2013. We were all waiting on another asteroid making a close pass of the Earth, when the Chelyabinsk meteoroid exploded 14 miles above the city. Over a thousand people were injured by the blast wave. They saw the bright flash and rushed to the windows to see what it was. Then the blast wave hit, shattering the windows, causing glass cuts for over a thousand people. One building’s wall collapsed, and a fragment fell into a lake outside of town.
NASA’s record in attempting to hit a planetary object dates back to the early 1960s and the nine Pioneer missions to crash a probe on the Moon, sending back pictures all the way down. Back in the early 60s, just hitting a 2,100-mile (3380 kilometer) wide object a quarter of a million miles away was a dicey prospect. It’s one thing to miss the Moon on one side or the other, but to not have enough oomph to even make it all the way is downright embarrassing. NASA did much better by the end of the decade with the Apollo manned landings and bombarding the Moon with used space vehicles for seismic studies of its interior.
NASA actually collided a spacecraft into a comet. That was July 4, 2005, when the impactor part of the Deep Impact spacecraft hit Comet Tempel 1’s nucleus, attempting to study part of its subsurface. The non-impactor part was later renamed EPOXI and went on to fly by the dog-bone shaped Hartley 2 comet nucleus. Another reused comet explorer spacecraft Stardust after collecting cometary dust from Comet Wild 2 (pronounced Vilt 2), and possible interstellar dust penetrating the solar system, and after dropping the sample re-entry capsule back on Earth it ended in solar orbit. Later it was repurposed as the Stardust-NexT mission and flew by Tempel 1 six years later to study the crater the Deep Impact Impactor made in the comet.
To study the effect of a collision of a spacecraft from the Earth despite the fact that Dimorphos cannot be seen is a trick. However, the pair is an eclipsing binary from our point of view, so the brightness of the unresolved pair changes as they eclipse each other.
Before the collision, Dimorphos had an 11.9 hour orbit of Didymos. Dimorphos is a fifth the size of Didymos orbiting it at three times the primary’s radius. If the orbit is near circular, Dimorphos’ orbital velocity is only 0.39 mph (0.63 kph). It should be relatively easy to see a tiny change in Dimorphos’ orbital period.

Last frame Dimorphos fit in from DART. Credit NASA / JHAPL.

Two images from the LiciaCube satellite launched from the DART spacecraft 15 days before the impact, and trailing it to record the collision with its wide and narrow angle imagers. Dimorphos does appear to be a rubble pile asteroid from its appearance and the amount of ejecta caused by the impact. The ejecta adds to the effect of the spacecraft’s kinetic energy by pushing away from the asteroid by Newton’s third law of motion. Credit: Italian Space Agency.

A frame from a time-lapse video taken from the ATLAS Project’s South African observatory of the unresolved Didymos – Dimorphos pair and the expanding ejecta cloud. The asteroid pair developed a dust tail like a comet for a while.
ATLAS is an acronym for a rather apocalyptic title “Asteroid Terrestrial-impact Last Alert System”. Developed by the University of Hawai’i and funded by NASA. It has two telescopes in Hawai’i, one in Chile, and one in South Africa. Credit: NASA/UH.

Days later, Dimorphos was exhibiting a thin dust tail, like a comet.

Now we wait on Earth’s observatories to observe of the period of Dimorphos’ orbit. It should decrease the orbital time.

09/26/2022 – Ephemeris – The DART spacecraft will attempt to deflect an asteroid tonight, Artemis I launch postponed

This is Ephemeris for Monday, September 26th. Today the Sun will be up for 11 hours and 57 minutes, setting at 7:32, and it will rise tomorrow at 7:35. The Moon, 1 day past new, will set at 8:07 this evening.

Tonight at 7:14 pm EDT (23:14 UTC), NASA’s DART spacecraft will collide with the tiny asteroid Dimorphos, which is orbiting the somewhat larger asteroid Didymos. They are potentially hazardous asteroids. The idea is to see what effect the collision has on the orbit of Dimorphos as it orbits Didymos at four tenths of a mile an hour. Trailing DART is an Italian CubeSat LiciaCube (pronounced LEE-cha-cube), which was launched from DART more 15 days ago to witness the collision. DART is an acronym for Double Asteroid Redirection Test, part of the Planetary Defense Program. Earth based radio and optical telescopes will assess if and how much the collision alters the orbit of Dimorphos. LICIAcube will return images of the collision, crater and the other side of Dimorphos. NASA will air it live on their channels.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

Unlike the Artemis I launch, this event cannot be postponed. It will either hit Dimorphos at 7:14 pm or miss forever.

Graphic on NASA’s DART mission to crash a small spacecraft into a mini-asteroid to change its trajectory as a test for any potentially dangerous asteroids in the future. Click on the image to enlarge it. Credit: AFP / AFP (Agence France-Presse)

A Note from EarthSky.org:

If you want to watch the event live, coverage begins at 6 p.m. EDT (22 UTC) on September 26, 2022, on NASA’s website. You can also watch it via Facebook, Twitter and YouTube.

Artemis I news

The Artemis I launch, scheduled for Tuesday, September 27, has been postponed due to the threat from tropical storm Ian.

09/12/2022 – Ephemeris – The Dart Mission hits its asteroid in two weeks

This is Bob Moler with Ephemeris for Monday, September 12th. Today the Sun will be up for 12 hours and 40 minutes, setting at 7:59, and it will rise tomorrow at 7:19. The Moon, 2 days past full, will rise at 9:16 this evening.

Two weeks from today, a small satellite will smash into a small asteroid ion an attempt to change its orbit. The spacecraft and the name of the NASA mission is DART (Double Asteroid Redirection Test). At 7:14 pm Monday, September 26th, the DART spacecraft will crash into a tiny 525-foot diameter asteroid that’s orbiting a larger asteroid. The target is Dimorphos that is orbiting Didymos. Dimorphos is orbiting Didymos at the slow pace of four tenths of a mile an hour, taking 11.9 hours to orbit it once. The DART spacecraft hit should change that a bit. A cube sat, launched by DART, should witness the event. Radio telescopes using radar should see any effect on the velocity of Dimorphos, to see if it worked.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

Schematic of the DART mission shows the impact on the moonlet of asteroid (65803) Didymos. Post-impact observations from Earth-based optical telescopes and planetary radar would, in turn, measure the change in the moonlet’s orbit about the parent body. The DART spacecraft is not to scale with the asteroids. Click on the image to enlarge it. Credits: NASA/Johns Hopkins Applied Physics Lab.

Dart and asteroids to scale with terrestrial landmarks. Click on the image to enlarge it. Credit: NASA/JHUAPL

11/23/2021 – Ephemeris – NASA to launch a mission to crash into an asteroid overnight tonight

This is Ephemeris for Tuesday, November 23rd. Today the Sun will be up for 9 hours and 17 minutes, setting at 5:07, and it will rise tomorrow at 7:51. The Moon, half-way from full to last quarter, will rise at 8:17 this evening.

As of last Sunday night, it was GO for launch of NASA’s DART Mission at 1:21 am Eastern Standard Time tomorrow morning on a Falcon 9 rocket from Vandenberg Space Force Base. DART stands for Double Asteroid Redirection Test. The DART spacecraft is to smash into a small asteroid named Dimorphos, that slowly orbits another somewhat larger asteroid, Didymos. Dimorphos orbits at only 7 inches per second, so even the smallest impact should alter the orbit noticeably. About a week before the planned collision, DART will release a small CubeSat to arrive 3 minutes after the collision to survey the crash site. In 2024 the European Space Agency will launch a satellite to survey the asteroid pair and note any long-term effects, to see if this technique for diverting asteroids is feasible.

Addendum

DART spacecraft with Dimorphos and Didymos. The DART spacecraft is not to scale with the asteroids. See below. CREDIT: NASA/JHUAPL

Dart and asteroids to scale with terrestrial landmarks. Credit: NASA/JHUAPL

10/19/2021 – Ephemeris – Introducing the DART mission

This is Bob Moler with Ephemeris for Tuesday, October 19th. Today the Sun will be up for 10 hours and 47 minutes, setting at 6:50, and it will rise tomorrow at 8:05. The Moon, 1 day before full, will set at 7:54 tomorrow morning.

Last Saturday morning, the Lucy mission to Jupiter’s Trojan Asteroids was launched. These asteroids are forever locked in Jupiter’s orbit and will never be a hazard to the Earth. Next month, NASA will hopefully launch a mission to a much closer asteroid Didymos, which is considered a potentially hazardous asteroid. The asteroid has a diameter of a bit less than a half mile (780 meters). It also has a satellite named Dimorphos, which has acquired the nickname Didymoon, 520 feet (160 meters) in diameter. The mission called DART for Double Asteroid Redirection Test will see how the impact of a spacecraft hitting the small Didymoon will affect its orbit around the larger asteroid.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT-4 hours). They may be different for your location.

Addendum

The Double Asteroid Redirection Test (DART) mission is NASA’s contribution to the international Asteroid Impact & Deflection Assessment (AIDA) program to determine the effectiveness of a spacecraft kinetic impact of an asteroid in altering its orbit. Credit: NASA.