Leaving Earth cover

In 2019 I obtained from my former publisher the last 30 copies of the now out-of-print hardback of Leaving Earth. I sold about half of these, and with only a handful left in stock I have raised the price. To get your own autographed copy of this rare collector's item please send a $75 check (includes $5 shipping) payable to Robert Zimmerman to

Behind The Black, c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

I will likely raise the price again when only ten books are left, so buy them now at this price while you still can!

Also available as an inexpensive ebook!

Leaving Earth: Space Stations, Rival Superpowers, and the Quest for Interplanetary Travel, can be purchased as an ebook everywhere for only $3.99 (before discount) at amazon, Barnes & Noble, all ebook vendors, or direct from my ebook publisher, ebookit.


Winner of the 2003 Eugene M. Emme Award of the American Astronautical Society.

"Leaving Earth is one of the best and certainly the most comprehensive summary of our drive into space that I have ever read. It will be invaluable to future scholars because it will tell them how the next chapter of human history opened." -- Arthur C. Clarke

Fading Martian slope streaks

Fading Martian slope streaks
Click for full image.

Cool image time! I’ve covered the topic of the mysterious slope streaks on Mars previously in great detail (see here and here). Essentially they are generally dark streaks (but sometimes light) that appear randomly on slopes and then fade over time. Unlike recurring slope lineae, another changing streak found on Martian slopes, the coming and going of slope streaks is not tied to the seasons. They can appear at any time in the year, and will take several Martian years to fade away.

The image to the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on March 26, 2020. It shows numerous slope streaks down the eastern interior rim of a crater in the transition zone between the northern lowlands and the southern cratered highlands in a region dubbed Arabia Terra.

Though I can find no previous high resolution image of this crater to measure any temporal changes, you can clearly see that this slope has experienced many streaks over time, with some darker than others. The different shades suggest that the lighter streaks are older and have faded, with the darker streaks more recent events.

At the moment there is no strong consensus on the causes of these streaks. As one science paper noted, “The processes that form slope streaks remain obscure. No proposed mechanism readily accounts for all of their observed characteristics and peculiarities.” We know they occur in equatorial regions and dusty locations, and that they are triggered by some disturbance at the topmost point of the streak, which then causes a chain reaction down the slope. Other than that, the facts are puzzling, and suggest that these streaks are a phenomenon wholly unique to Mars.

The crater itself, located at 24 degrees north latitude, has some other mysteries. The features on its floor, for instance, are very puzzling. Though suggestive of the buried glaciers found in many craters in the mid-latitudes, this crater is a bit too far south. Maybe its higher altitude allows for some ice to remain here? Then again, the features on that floor might have nothing to do with ice. Maybe we are looking at sand carved by wind? Or hardened mud that was once wet?

I am merely guessing, a dangerous thing to do when one’s knowledge is limited. Then again, it’s fun, so please join in with your own guesses.

Pioneer cover

From the press release: From the moment he is handed a possibility of making the first alien contact, Saunders Maxwell decides he will do it, even if doing so takes him through hell and back.

Unfortunately, that is exactly where that journey takes him.

The vision that Zimmerman paints of vibrant human colonies on the Moon, Mars, the asteroids, and beyond, indomitably fighting the harsh lifeless environment of space to build new societies, captures perfectly the emerging space race we see today.

He also captures in Pioneer the heart of the human spirit, willing to push forward no matter the odds, no matter the cost. It is that spirit that will make the exploration of the heavens possible, forever, into the never-ending future.

Available everywhere for $3.99 (before discount) at amazon, Barnes & Noble, all ebook vendors, or direct from the ebook publisher, ebookit.


  • John

    They’re probably just subterranean spore colonies bursting from the regolith when surface conditions are just right. Probably.

  • Jeff

    I could see wind eroding dust around a small pebble at top of steep slope, gravity finally taking over and the pebble rolls downhill bumping into its neighbors. And so on…

  • Kelly

    I think the uncertainty has to do with how flows behave under different gravitational accelerations. We know there are significant differences in flow behavior when we observe celestial bodies with accelerations not equal to Earth’s. For that reason, it may be difficult to resolve without having people on site to examine, test samples and excavate the top of the flow.

  • sippin_bourbon

    I always find Kodo drums rather relaxing.

  • someone

    Obviously, its from the Sand Worms…

  • mpthompson

    Is it possible that within the next few decades the cost of transportation to Mars can be reduced to the point that a probe dedicated to researching phenomena such as this can be sent to a specific site to really understand what is going on? Perhaps a combination rover, driller and flying drone working together to understand the full picture.

    I can imagine NASA sponsoring the development of commodity technologies so that a university research department can assemble such a probe from off-the-shelf hardware, have it shipped to Mars via SpaceX hauling services for an affordable price, dropped in the vicinity by a global transportation service and finally using Starlink-style Internet communication network for remote operation and telemetry.

    Imagine how much research could be done on Mars if such a probe could be built and deployed for say a $5M to $20M price. The most valuable part is really the data that is returned, but in developing the infrastructure that would make such a dedicated mission feasible at an affordable price.

  • Jeff: Slope streaks are not avalanches. Make sure you read the two previous posts about them, the links of which are included in this post. They do not change the topography at all.

  • Kelly: As I mentioned above, make sure you read my two previous posts on slope streaks, linked to in this post. You will understand how really puzzling these things are.

  • Cotour

    On the subject of crazy geology:

    https://youtu.be/3q-qfNlEP4A 21min.

    Quick clay landslide at Risaa, very interesting.

    Ancient glacial sea clay deposits when the salt is leached out over thousands of years liquifies instantly when disturbed. Brace for destruction.

  • Star Bird

    Marvin and K-9 are coming to Earth looking for specimen ti take back for Study we should let them have Robert DeNiro his walnut Brain needs to be analized

  • Thanks very nice blog!

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