The Solar System is a-Changing

By Corey S. Powell | March 31, 2016 11:14 pm
Three of the five big impacts (that we know of!) on Jupiter over the past 22 years. Comet Shoemaker-Levy 9 left a series of huge blemishes (left), but the less celebrated 2009 strike left scars of its own (middle). Two weeks ago, Gerrit Kernbauer of Austria caught another impact in the act (right). Credit: ESA/NASA/STScI; Anthony Wesley; Gerrit Kernbauer.

Three of the five impacts observed on Jupiter over the past 22 years: Comet Shoemaker-Levy 9 left a series of huge blemishes (left). The less celebrated 2009 strike created scars of its own (middle). Two weeks ago, Gerrit Kernbauer of Austria caught an impact in the act (right). Credit: ESA/NASA/STScI; Anthony Wesley; Gerrit Kernbauer.

When I was a kid and got hooked on astronomy (sometime around age 7), one of the things I deeply enjoyed about the night sky was its constancy. The human world is full of unwanted variables: Families move, friends get into fights with you, bicycles crash, birthday parties don’t turn out the way you wanted…but all you have to do is look up and you can make contact with another realm that never produces such disappointments. The stars are always in the same places. The planets slide around in the sky, but they don’t really change. Every time you see Jupiter, it is the same old reliable Jupiter.

Except that it isn’t. The closer you look at the solar system, the more you see change happening, and on all time scales. The constancy was an illusion, created by humans (not just my younger self!) watching the sky too erratically and too impatiently to see what is really going on. Jupiter is not always the same old Jupiter, as is abundantly clear from amateur video showing the planet getting whacked by a small asteroid or comet on the night of March 17. Watch other worlds and you’ll see the same thing happening. Wait longer–quite long by human standards, but very short in astronomical terms–and some really weird, extreme events unfold.

But I’m getting ahead of myself here.

The shooting gallery. Even as a child I understood that there were some rule-breakers. Meteors are ephemeral, and comets come and go. Mars has seasons; Jupiter’s stormy red spot moves around and varies in color. As the years went by, astronomers became increasingly aware of the role of comets and asteroids in an ongoing, more intense reshaping of the solar system. Jupiter was once again the great planetary showcase: In 1992, its gravity shattered Comet Shoemaker-Levy 9 and then two years later, in July 1994, the 21 cometary fragments slammed into the giant planet.

The effects were dramatic, as multiple enormous blemishes appeared atop Jupiter’s banded clouds. Worldwide observations of the event provided a bonanza of scientific information about comet impacts; they also delivered an utter affront to the notion of constancy in the solar system.

The collision of Shoemaker-Levy 9 was the first direct observation of a major solar system impact, but hardly the last. Amateur astronomers have since observed five more impacts on Jupiter, though none of these were predicted in advance so they were not studied with anything like the detail of the 1994 fireworks. Flashes of light from these celestial disruptions appeared in 2009, twice in 2010, in 2012, and now in the intriguing observations from two weeks ago.

It’s safe to assume that impacts like these have been occurring all along, just without anyone noticing. It’s also safe to assume that the actual frequency of hits is quite a bit higher than what’s been documented, since nobody would see impacts that occur on the farside of the planet, or ones that simply happen to occur during daylight hours in the locations where most amateur astronomers are looking.

A new 110-foot crater appeared on the moon on September 11, 2013. The Moon Impacts Detection and Analysis System picked up the flash of impact. (Credit: NASA/GSFC/Arizona State University)

A new 110-foot crater appeared on the moon on September 11, 2013. The Moon Impacts Detection and Analysis System picked up the flash of impact. (Credit: NASA/GSFC/Arizona State University)

Naturally, impacts are happening all the time on other worlds as well. And now we have the tools and techniques to see them. NASA’s Automated Lunar and Meteor Observatory has recorded hundreds of flashes from the impact of large meteoroids on the moon (“large” in this context means a few ounces or more, sometimes much more). These strikes can produce easily visible craters, as shown above. Unlike the scarring on Jupiter’s clouds, such changes are essentially permanent. Even a small lunar crater should remain evident for millions of years, if not billions.marscrater_shareable-full

The sizable fleet of spacecraft constantly observing Mars means that scientists now have the tools to notice fresh impact there, too. As a result, we can see the Red Planet transforming right before our eyes. More than 400 new craters have been recorded, mostly over the past decade; a major impact in 2012 produced a 150-foot pit, landslides, and a 5-mile-wide zone of debris.

Bigger bangs. All of the changes I’ve described so far, dramatic as they may be, still don’t fundamentally alter the appearance of the solar system. A more pockmarked Mars still looks like the Mars we know, and on the timescale of a single lifetime my original sense of permanence is still reasonably accurate. But if you keep running the clock, even that kind of reliability vanishes.

What if Mars was surrounded by rings, like the rings of Saturn? That would certainly be a stunning change to the landscape of our planetary neighborhood. And it’s really going to happen, in approximately 20 million years. The planet’s inner moon, Phobos, is on an inward-spiraling trajectory. Eventually it will come so close that Mars’s gravity will shred it into rubble, which will spread out into rings as massive as the ones around Saturn. The rings of Mars might persist for a few hundred million years, and they should make a lovely sight for future generations.


Presenting Mars circa 20 million AD, when its moon Phobos will have broken up into rings. (Credit: Tushar Mittal/Celestia Development Team)

And what if Saturn didn’t have those dramatic rings? That may have been the case not so long ago. According to a provocative new model, the entire ring system, along with the currently existing inner satellites of Saturn, are less than 100 million years old–just 2 percent the age of the solar system. If we had lived at the time of the dinosaurs, we would have peered through our telescopes at a ringless Saturn, a rather drab yellow ball.

My modern self finds the idea of continual celestial evolution exciting to contemplate. But a little part of my 7-year-old self persists, mourning for a constancy that does not really exist anywhere, not even in space.

Follow me on Twitter for astronomy and other science news: @coreyspowell


  • OWilson

    I would guess that you, like me, grew up in a location where you could just look up and see the constellations on most nights. That’s how I got hooked.

    Where I live now the stars have virtually disappeared in the light pollution.

    I feel sorry for the kids today, who don’t have the opportunity that we had.

    If you get a chance to see the sky in all its splendor you’ll immediately see why the ancients worshiped them. They actually DID rule the heavens!

    If you get a really big sky, clear and dark, you will almost have the sensation to cover your head from those huge hanging objects that look like they could drop on you at any moment.

    • coreyspowell

      Beautifully said. Thank you!

      • OWilson


        The only complaint is that your articles are too few and far between. We look forward to them!

        They tend to settle down the overblown rhetoric (yep, from me too :) that pervades these blogs, and reminds us that we really do live in a “miracle” universe by any definition of the word.

  • Uncle Al

    A major NASA priority must be to de-orbit Phobos into its Roche limit. Phobos’ semi-major orbital radius is 9376 km (5989 km from Mars’ surface) and masses 10.6×10^15 kg. Install a great circle-wound, small radius (2.65×10^(-8) ohm-meter), aluminum (density re transport) wire solenoid, then enjoy solar wind inductance (re Parker spiral). Figure about 3×10^(-10) tesla ambient space from solar wind plus local planetary magnetic field.

    Lay down a vast swath ribbon of parallel spaced aluminum wires (no insulation necessary). When you return to start, stagger the connections by one. Repeat as necessary. Finally, connect the far ends.

    • Martin Marty マ (m)

      Could you put that in Star Trek metaphor terms for those of us too lazy to google 90% of those terms? Thanks. :)

      Stop phobos crashing and use it as a battery, for example…

  • mamun

    this is really very good article.
    Thanks mr. Corey S. Powell

  • Elaflamme

    Impact craters? Hmmmm… What impacted? It was a lighting bolt that did the impacting. Yes it makes sense now and fits the evidence perfectly!

  • Mike Richardson

    I’m lucky enough to live where you can still see the Milky Way at night, but I can recall the night sky being even darker when I was younger. The Little Dipper could be spotted, along with its bigger cousin. Light pollution does extend to the suburbs and the country these days though, at least on the horizon. Not the kind of transience that you like when talking about astronomy, but one that impacts most of us. As for the objects in the sky themselves, I’ve been able to see transits of Jupiter’s moons through my telescope, but I haven’t been one of the fortunate few to see it take a beating from a comet. At least Jupiter can heal its scars pretty quickly, being a gas giant instead of a solid body like Mars or the moon. Something else changing on Jupiter — the Great Red Spot. It’s been getting smaller over the last few decades, raising the question of how permanent it actually is. Still, for a storm, a few centuries is a good run by any stretch.


Out There

Notes from the far edge of space, astronomy, and physics.

About Corey S. Powell

Corey S. Powell is DISCOVER's Editor at Large and former Editor in Chief. Previously he has sat on the board of editors of Scientific American, taught science journalism at NYU, and been fired from NASA. Corey is the author of "20 Ways the World Could End," one of the first doomsday manuals, and "God in the Equation," an examination of the spiritual impulse in modern cosmology. He lives in Brooklyn, under nearly starless skies.


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