for Mars as well as Earth the rule-of thumb is about 20:1 between impactor and crater, so that 470 foot diameter crater corresponds to a 23.5 foot impactor (why quote 468 feet? do they claim 0.5% precision in measurement?). (things like that burn up in Earth's atmosphere on a regular but infrequent basis) It would be a good meteor, but no Tunguska.
Another rule of thumb for planets with atmospheres is that it needs a projectile with original diameter comparable to the "thickness" of the atmosphere to penetrate. Now that "thickness" is not the actual depth of the atmosphere, but is the depth you would get if you froze it all out and plated it on the surface. The scientific concept of "amagads" is a way of measuring atmospheres in terms of this "thickness" - it avoids issues of pressure vs gravity.
Equivalently, the atmospheric "thickness" can be expressed as the height of a liquid water barometer [as measured on that planet] - about 30 feet for the Earth. Again, this sidesteps the issue of different gravity on different worlds.
Space/Science » in reply to re: Also some brand new impact craters!
20:1
The whole thread (61 posts)
- Now what? Another NASA "significant find" briefing coming up.
- So how long before MRO can get a good look at it?
- Way off topic posts removed.
- were those posts by any chance my posts?
- Yup
- If NASA schedules the announcement of bogus claims about water on Mars to coincide with the release of bad news from Iraq, then it belongs right here
- Yup
- were those posts by any chance my posts?
- I've seen these in the mountains...
- re: So what? Another NASA "significant find" briefing coming up.
- Back and forth, back and forth, back and forth
- Why water (vs dry/gas flow)?
- A little more (big pic)
- Also some brand new impact craters! (n/t)
- Briefing on now (10 AM Pacific). Liquid water flow. (n/t)
- MGS Relayed Picture Of Great Galactic Ghoul Before Being Gobbled Up?
- Scuttlebutt: Liquid water (n/t)