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Lucy (the spacecraft) is all set for a close flyby of asteroid Donaldjohanson today [1]
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Date: 2025-04-20
Let’s take a few moments off the numbing news cycle to marvel at the amazing beauty of the cosmos and humankind’s quest to understand it.
NASA's Lucy spacecraft, which was launched on October 16, 2021, is getting ready for its close flyby of the asteroid named Donaldjohanson today, April 20, at 1:51 p.m. EDT (17:51 UTC). www.nasa.gov/...
Donaldjohanson is a relatively large (about 3.9 km wide) main belt asteroid, orbiting the sun between the orbits of Mars and Jupiter, which was selected for Lucy’s 2nd encounter with an asteroid.
Lucy will use this encounter to test its instruments and tracking systems, in preparation for its main mission of surveying 7 Jupiter Trojan asteroids in 2027-2033.
There will be no live images during the flyby; they will be downloaded after the spacecraft is well past the asteroid and the antenna is pointed back towards earth.
The Donaldjohanson flyby
Currently, Lucy and asteroid Donaldjohanson are located just beyond Mars, at a distance of ~223 million km from earth. Signal travel time between Lucy and earth is ~12 minutes. See map below.
Lucy will get within 960 km of the surface of asteroid Donaldjohanson and pass it at a relative speed of 48,240 km/h.
About 30 minutes before closest approach, Lucy will orient itself to track the asteroid, turning its high-gain antenna away from Earth. All three science instruments – the high-resolution greyscale imager called L’LORRI, the color imager and infrared spectrometer called L’Ralph, and the far infrared spectrometer called L’TES, will be active.
40 seconds before closest approach, Lucy will stop tracking DJ to protect its sensitive instruments from the Sun.
Communications link will be established about an hour later.
The Lucy Mission
Lucy is a NASA mission to explore the Trojan asteroids located in Jupiter's orbit. Along its journey, it will also explore two asteroids in the main asteroid belt between Mars and Jupiter.
Here is a graphic illustrating Lucy’s trajectory over its 12-year mission.
Oct 16, 2021: Launch
Nov 11, 2023: flyby of main belt asteroid Dinkinesh
April 20, 2025: flyby of main belt asteroid Donaldjohanson
2027-2028: survey five L4 Trojan asteroids
2030: 3rd flyby of earth
2033: visit two L5 Trojans
Asteroid Donaldjohanson
Asteroid Donaldjohanson is part of the main belt of asteroids located between the orbits of Mars and Jupiter. It is a fragment of a collision 150 million years ago that produced the Erigone family of asteroids.
Distance from Sun : 1.936 - 2.830 AU
Orbital period: 3.68 yr (1,343 days)
Mean diameter: 3.895 km
Rotation period: 252 hours
Donaldjohanson's periodically varying lightcurve suggests that it must either be highly elongated in shape or have a satellite companion. Stay tuned!
Asteroid Dinkinesh
On Nov. 1, 2023, Lucy flew fly and took some amazing pictures of Asteroid Dinkinesh. It also discovered that the asteroid has a small companion, which was given the name Selam. www.nasa.gov/...
Below is a pair of stereoscopic images of the asteroid Dinkinesh and its satellite, Selam, created using data collected by the L’LORRI camera on the NASA Lucy spacecraft in the minutes around closest approach on Nov. 1, 2023. To use this image pair to get a better sense of the 3D structure of the asteroids, either relax the axes of your eyes, as if staring through the screen to infinity (so that you are looking at the left image with your left eye and the right image with your right eye), or use stereoscopic glasses.
blogs.nasa.gov/…
Credit: NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab for the original images/Brian May/Claudia Manzoni for stereo processing of the images.
The Trojans
The Jupiter Trojans (aka Trojan asteroids) are a group of asteroids located in Jupiter's orbit around the Sun.
The group known as the Greeks are located around the L4 Lagrange point, 60° ahead of Jupiter, the Trojans are located around the L5 Lagrange point, 60° behind.
The main belt asteroids lie between the orbits of Mars and Jupiter.
There are millions of asteroids between here and Jupiter and trillions of icy ones beyond the orbit of Pluto. Only the nearest and largest ones have been catalogued.
Why visit these asteroids?
From lucy.swri.edu/… - Planet formation and evolution models suggest that the Trojan asteroids are likely remnant of the same primordial material that formed the outer planets, and thus serve as time capsules from the birth of our Solar System over 4 billion years ago. These primitive bodies hold vital clues to deciphering the history of our Solar System and may even tell us about the origins of organic materials—and even life—on Earth.
What’s in a name?
The Lucy mission is named after the Lucy hominin fossils, which were discovered in 1974 in Ethiopia and are dated to about 3.2 million years ago.
Why Lucy? According to NASA, “just as that Lucy fossil provided unique insights into humanity’s evolution, the Lucy mission promises to revolutionize our knowledge of planetary origins and the formation of the Solar System.”
Lucy skeleton (AL 288-1) Australopithecus afarensis, cast from Museum national d'histoire naturelle, Paris
Reconstruction of Lucy at the National Museum of Anthropology in Mexico
en.wikipedia.org/...
Dinkinesh is the Ethiopian name for the Lucy fossil. The name means "you are wonderful" in the Amharic language.
Asteroid (52246) Donaldjohanson is named after one of the co-discoverers of the Lucy fossil.
The names for these two asteroids were recommended by the Lucy team.
The moonlet discovered during the Lucy mission encounter with asteroid Dinkinesh was named - “Selam” or ሰላም, which means “peace” in the Ethiopian language Amharic.
Selam is the name of a fossil of a 3-year-old Australopithecus afarensis female hominin, whose bones were first found in Dikika, Ethiopia in 2000. Nicknamed Lucy's baby, the specimen is actually 120K years older than "Lucy", who lived 3.2 mya.
Interestingly, the Lucy hominid was named after the 1967 Beatles song "Lucy in the Sky with Diamonds". The song was played loudly and repeatedly in the expedition camp all evening after the excavation team's first day of work on the recovery site.
And yes the Lucy spacecraft has a diamond, a large lab-grown diamond in its L'TES instrument, which serves as a beamsplitter.
So, let's listen to the Beatles sing “Lucy in the sky with diamonds” as Lucy flies by asteroid 'you are wonderful' Dinkinesh in this video with some interesting graphics (warning: contains sharp flashes of light and images).
x YouTube Video
The Plaque
The Lucy spacecraft carries a plaque, following the tradition set by the Voyager spacecraft, which serves as a time capsule with messages from prominent thinkers of our time and a diagram showing the positions of the planets on the date of Lucy’s launch.
After the mission is over, the Lucy spacecraft will remain in a stable orbit between Earth and the Trojan asteroids. Lucy’s designers expect that some day in the distant future our descendants may retrieve the Lucy spacecraft and read our messages.
Among the messages is one by Carl Sagan that is very relevant for the present time, as the trump regime is planning to cut NASA’s science funding by half and has gutted science programs in many other agencies -
Cutting off fundamental, curiosity-driven science is like eating the seed corn. We may have a little more to eat next winter but what will we plant so we and our children will have enough to get through the winters to come?
Epilogue
While we marvel at the universe and search for our origins on this Easter Sunday, let’s keep in mind that there is a small segment of humanity, esp. in this country, that cares two hoots about science except when it enriches them and when it allows them to control the minds of millions of ordinary folks and turn them into zombies. Let’s make sure that humanity survives and flourishes, guided by the light of science, not by the darkness of these soulless creatures. Let’s keep working to educate the public, keep them informed and let’s keep stressing that the survival of humanity depends on science, education and on electing Democrats.
References
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