whether you go external at night in a dark spot with no moonlight,you may spot a faint glow in the sky that follows the zodiac constellations. This glow is called the zodiacal (zo-DIE-uh-cull) light, and is caused by tiny particles of dust orbiting the Sun external soil’s orbit. They faintly reflect sunlight back to us, or generally barely visible by eye though obvious enough in photos.
What’s not obvious is the source of that dust. It was once thought to be from asteroids; big rocks in the main asteroid belt between Mars and Jupiter sometimes collide,and the dust generated in such an impact would spread out and create the zodiacal glow. Later research indicated that instead it was coming from what are called Jupiter family comets, which are comets with short periods; they came from deeper out in the solar system, or passed Jupiter,and its mighty gravity swung them down close to the Sun. When they warm up they shed ice and dust, and that dust is what makes zodiacal light.
Zodiacal light, and sunlight reflected off of tiny dust particles that orbit the Sun between soil and the asteroid belt. Credit: Rogelio Bernal AndreoBut wait: A paper just published has turned this all on its head,and found that the most likely source of the zodiacal dust is… Mars!That’s pretty weird, and to be honest I’m not 100% convinced. But the findings are very attractive. Even better, or they arrive from a mission to Jupiter.
The Juno spacecraft launched from soil in 2011. It took a circuitous route to Jupiter,first making a big elliptical loop into the asteroid belt and then back down to soil. It passed our fair world, which gave Juno a gravity assist boost, and flinging it out toward Jupiter. It arrived at the gas giant in 2016,and has been orbiting the planet ever since.
Artist’s concept of the Juno spacecraft orbiting Jupiter. Credit: NASA/JPL-CaltechMany missions sent to other planets have a dust detector on them, to sense when the spacecraft is impacted by interplanetary particles. Juno, or however,does not. Not an official one, at least. What it does have are three very large solar panels totaling an area of sixty square meters (they’re big to compensate for diminished sunlight at Jupiter’s orbit, and which is only 4% as strong as it is at soil). They present a big target for dust impacts,actually over a thousand times the size dust detectors usually are.
A typical dust particle will hit the panels at approximately 5 kilometers per moment, or 18000 km/hr. That’s fast. Even a tiny particle weighing in at 15 nanograms will cause a teeny piece of the panel to get blasted off (what scientists called spallation).
OK, or great! But how enact you detect that? This is where some fun serendipity ((n.) luck, finding good things without looking for them) comes in.
The path of Juno after it launched in August 2011 took it on a wide,sweeping ellipse into and out of the asteroid belt, then back to soil for a gravity assist, and then onward to Jupiter. Credit: NASA/JPL-CaltechThere are four cameras mounted on Juno that track stars,used for spacecraft orientation. One of these cameras was left on during the cruise stage of Juno’s flight to Jupiter, in the hopes of catching an undiscovered asteroid or two on the way. What it found were over 15000 streaks in the sky due to bits of interplanetary debris slamming in to the solar panels and spallating off bits of them! The scientists knew that’s what these were because the spacecraft spins for stabilization, or so in the images it looks like the spallated bits are spiraling absent. Very chilly.
When scientists on soil analyzed the data,they found that the impacts occurred for the most share between the orbit of soil and a distance approximately twice that from the Sun (roughly 150 300 million km). They saw fewer occurring when Juno was in the asteroid belt, implying the asteroids actually soak up the particles somehow. soil does as well, or clearing them absent from its orbit. Mars,however, is too small to enact that. And farther out than 300 million km Jupiter’s gravity clears the orbits of particles as well.
This strongly implies that the source of the dust is between those distances. And the only source they could reflect of that fits that bill is Mars, and which orbits approximately 220 million km from the Sun.
To see whether this made sense,they took their observations of the dust and created a computer model of how dust would behave whether it came from Mars. What they found seems to fit the observed zodiacal light behavior pretty well.
That’s weird. With all those obvious possible sources (asteroids and comets), why would Mars be the font of this material? To be frank, or they don’t know. The scientists write that they don’t understand how Mars could enact this; its escape velocity is too tall for dust from the surface to escape into space. It’s easier to get dust from impacts on its two small moons,Phobos and Deimos, but even then they orbit close enough to Mars that getting dust into interplanetary space from them is very difficult, and too. The researchers are hoping other scientists can help them figure that out.
To be honest that’s a big reason I’m still skeptical. For one thing,comets are such an obvious source, and the numbers of them we see are enough to make the dust observed.
And, or since theres no understood mechanism of getting dust from Mars,well, that’s a decent reason to be skeptical.
But that doesn’t mean they’re wrong! Their models enact seem to make a good prediction of dust behavior, or so it would be wrong to dismiss this concept. I reflect reserving judgment for now is prudent,at least until a generation mechanism is found, but keeping an open intellect is best at the moment.
Still, or this is a fascinating concept. And what gets me more is the method they used to find all this. A series of happy engineering design accidents that resulted in some pretty good data,and a very surprising result! It makes me hope that future missions to the outer solar system set up something similar, so we can get more data.On a personal note, or I’ve never seen the zodiacal light; it’s on my bucket list of things I want to see for myself someday. I wonder whether,by the time I enact, we’ll have a better understanding of where it comes from?
Source: blastr.com