Scroll down to read this post.

 

Please consider supporting my work here at Behind The Black by giving either a one-time contribution or a regular subscription, in any one of the following ways:

 

1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.

 

2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
 

3. A Paypal Donation:

4. A Paypal subscription:


5. Donate by check, payable to Robert Zimmerman and mailed to
 
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652


Craters, craters, everywhere

Below the fold are two images released today, one from Dawn at Vesta and the other from Messenger at Mercury. What makes them interesting to me is that, though the surfaces of both Vesta and Mercury are crater-packed, there are definitely distinct differences between them that one can spot if you look closely, all highlighting the fundamentally different environments of both worlds.

First, the Vesta photograph. The image looks out past the asteroid’s horizon, showing clearly that this dwarf planet is not spherical, with the south pole depression that puzzles scientists just on the planet’s limb. The parallel long deep grooves that are associated with this depression can be seen on the right. Notice also that the inside walls of all the craters slope downward in a very shallow manner. This gives the impression that the impacts that formed these craters smashed into an almost beachlike sandy surface. Note too the that the center of some craters have what appear to be flat small “ponds,” a phenomenon seen by the spacecraft NEAR when it orbited the asteroid Eros. These ponds are not liquid, but are actually made up of fine-grained particles that settle in the hollows of the asteroid.

Vesta

For Vesta, these effects probably come from the asteroid’s relatively low gravity, which acts to keep the overall density of its material low.

Then there is the Messenger image looking east across a cratered Mercury plain. Here the craters generally appear to be more shallow, at least relative to the surrounding terrain. Also, the terrain seems more rounded and worn, its rough edges smoothed by eons of wear from the solar wind and the harsh radiation of the nearby sun. In fact, the largest crater in the image (filling the right-bottom quarter of the picture) has almost vanished with wear over time. You can also see one of Mercury’s unique scarps cutting through the crater at the top of the image. These scarps were created as Mercury slowly solidified and shrank.

Mercury craters

While both worlds appear very similar at first glance, this quick close look illustrates once again a very consistent finding by planetary scientists since the beginning of the space age: every object orbiting the sun is uniquely different, sometimes wildly so. Because of this scientists have learned never to be surprised by what they see once they get a chance to take a close look.

For this reason, expect some big surprises when New Horizons finally flies past Pluto in July 2015.

Share

Conscious Choice cover

Now available in hardback and paperback as well as ebook!

 

From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

 
Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.

 

“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.

 

All editions available at Amazon, Barnes & Noble, and all book vendors. The ebook can be purchased direct from my ebook publisher, ebookit, in which case you don't support the big tech companies and I get a bigger cut much sooner. Note that the price for the ebook, $3.99, goes up to $5.99 on September 1, 2022.

 

Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95). Just email me at zimmerman @ nasw dot org.

One comment

  • A. A gap is located at an average orbital distance, and asteroid orbits often have large eccentricities.
    B. They are held in place by resonances with other asteroids.
    C.Jupiter’s gravitational tugs keep them there.
    D.Actually, we never see asteroids in the gaps.
    E.They are kept in place by shepherding asteroids.

Readers: the rules for commenting!

 

No registration is required. I welcome all opinions, even those that strongly criticize my commentary.

 

However, name-calling and obscenities will not be tolerated. First time offenders who are new to the site will be warned. Second time offenders or first time offenders who have been here awhile will be suspended for a week. After that, I will ban you. Period.

 

Note also that first time commenters as well as any comment with more than one link will be placed in moderation for my approval. Be patient, I will get to it.

Leave a Reply

Your email address will not be published.