Earth and Moon from Space, from Hera
Earth and Moon from Space, from Hera https://asteroidday-uploads.s3.eu-central-1.amazonaws.com/wp-content/uploads/2024/10/25112355/Capture-decran-2024-10-25-a-11.23.48.png 1276 748 Asteroid Day https://asteroidday-uploads.s3.eu-central-1.amazonaws.com/wp-content/uploads/2024/10/25112355/Capture-decran-2024-10-25-a-11.23.48.png
Goodbye photos from an asteroid-bound spacecraft, plus the Sun is at its activity peak now
This article was originally published in the Bad Astronomy Newsletter (October 21, 2024 Issue #789) by Phil Plait, an astronomer and science communicator, as well as a friend of Asteroid Day.
Pic o’ the Letter
A cool or lovely or mind-bending astronomical image/video with a description so you can grok it
I love images of Earth and the Moon from space, especially when they’re a promise of things to come.
On September 26, 2022, NASA slammed the DART spacecraft into the tiny asteroid moon Dimorphos. The impact was designed to alter the 170-meter-long rock’s orbit around its parent asteroid Didymos enough to measure, and it was a success! It proved we can alter the trajectory of an asteroid should one be headed toward Earth. The impact itself also carved out a big crater in the little moon and ejected lots of debris into space.
Of course, once that happened there was no more DART to get follow-up data. It was vaporized upon impact. So in partnership with NASA, on October 7, 2024 the European Space Agency launched Hera, a spacecraft equipped with 12 different scientific instruments to take a close-up look at Dimorphos and see what happened to it. What substances were dredged up in the impact from under the surface? How big is the crater? What shape is it? What happened to the rest of the moon after the impact?
It will reach the asteroid system in December 2026. But as it left Earth engineers turned the spacecraft’s instruments towards our planet and took a series of shots to test things out.
Earth and the Moon from Hera’s Asteroid Framing Camera. Credit: ESA
Our home planet and its one (permanent) natural satellite were seen from 1.6 million kilometers away using Hera’s Asteroid Framing Camera, a low-resolution imager that will be used for navigation and some science. In this shot, the dayside of Earth is dominated by the Pacific Ocean.
One thing to note is how much brighter Earth is than the Moon. On average Earth reflects about 40% of sunlight that hits it, and the Moon only about 15% or less. It’s always amazing to me how contrast there is when the two are in the same shot.Also, from this distance, our planet is about as big as seen from the spacecraft as the Moon is by eye standing on Earth. Just for scale.
Earth and Moon, this time with Hera’s Thermal Infrared Imager. Credit: ESA
This shot was from Hera’s Thermal Infrared Imager, or TIRI. See anything weird about it?
Earth looks full, but the Moon only half full! That’s because this infrared camera is sensitive to wavelengths of light emitted by warm objects. The side of Earth facing the Sun is warmer than the night side, but in general only by a couple of dozen degrees. On the Moon the contrast is actually several hundred degrees, so the night side is much colder, and doesn’t emit much infrared light at these wavelengths, making it look dark. That’s wild.
Another thing I love about this image? It makes Earth look like every planet ever seen in Space:1999.
Finally, this is what our home looks like via Hera’s Hyperscout H instrument:
Earth and Moon with Hera’s Thermal Infrared Imager. Credit: ESA
Hyperscout H detects light that looks red to our eye out into the near-infrared, in 25 distinct colors. Different minerals absorb different colors of light from the Sun, so this will be used to map out what’s on the surface of Dimorphos and the locations. It doesn’t have fantastic spatial resolution (although, for comparison, it’s about twice as sharp as the human eye’s), so Earth looks fuzzy, but once Hera is close to the asteroid it will provide lovely information on what lies on the surface.
There is something poignant and beautiful about images like these, postcards taken from a voyage on its way out. Hera will never return to Earth, but instead make its new home orbiting Dimorphos. I’m really excited to see what happened there!
Astro Tidbit
A brief synopsis of some interesting astronomy/science news
It’s official: the Sun has reached its magnetic peak for this cycle, called solar maximum. To be clear this doesn’t mean we’ll start seeing less activity immediately. The cycle is…complex.
The Sun’s magnetism is generated deep inside, where moving parcels of ionized plasma (gas that’s lost one or more electrons) move around — it’s a bit of fundamental physics that A moving charge generates a magnetic field. Unlike Earth, which has a simple dipole field (with a north and south pole, like a bar magnet), the Sun has thousands of individual fields inside it.
Over time, the strength of these overall fields waxes and wanes. It’s an 11-year cycle of strength, going from weak to strong and back to weak again every 11 years. At the end of that cycle the Sun’s polarity reverse, with south becoming north and vice-versa, so really it’s a 22-year cycle.
The sunspot numbers over the past few centuries. Note that many of the maxima have double peaks. Credit: SILSO
Anyway, we’ve been nearing the peak for some time, and the magnetic activity has been on the increase. That means more sunspots, more solar flares, and more coronal mass ejections, which in turn means more activity at Earth, like increased radio interference, more aurorae, and possible serious interactions like blackouts (as happened in Quebec 1989).
But the Sun doesn’t just hit a peak and then start to weaken. The peak can last for years! And usually there’s a slight dip in strength before it rallies again, so the peak is really a double peak. Historically, the biggest flares and such happen after the peak, too, so we’re likely going to see a lot of activity for a while yet. Probably a year, maybe longer.
So if you missed the huge aurorae in May and again in October, you’ll likely get more chances. The Sun is not likely to start resting any time soon.
