Transcript Mercury’s Craters - Lunar and Planetary Laboratory

Mercury’s Craters
How They Are And What
They Are
Lindsay Johannessen
PTYS 495
From the Beginning…
o How do craters form?
o What kinds of craters are there?
o What are the circumstances of how these
craters form?
o What does this tell us about our history?
On Mercury, How Is It
Different?
o Most common types?
o Dispersion throughout region and
numbers!
o The biggies… Why are they so
interesting?
o Amazing effects on Mercury!
How Do Craters Form?
o Craters occur on any and every solid
bodied mass in the Universe.
o Craters’ shapes and sizes depend on
three things:
- Mass density of projectile object
and of impacted surface.
- Diameter of projectile object.
- Velocity of projectile object.
What Kinds Exist?
Simple Craters:
Single ridged with ejectoblanket
No caving rims
Retains excavation stage shape
Complex Craters
Have central peak
Outer rims collapse to enlarge diameter
Larger in general
Double and Multi-ringed Craters
Larger than central peak complex
Have second (sometimes multi) internal ring
caused from reverberation of impact
Formation of Simple Craters
Impact occurs
Seismic waves travel through
impactor and impacted
Crush, melt and vaporize most
of the impactor
Excavation crater is left
as main crater
Formation of Complex
Craters
Same initial process as
simple craters
From bigger impacts come
bigger results
Central peak and secondary
Rings form from reverberation
of initial impact
What These Craters Tell Us
Given consistent information:
Date ranges for bombardment periods
Possible surface structure
Quantifiable forces involved in impacts
Mercurian Craters
Generally larger and more violent than what
we usually see in our Solar System
Mercury’s Gravitational Pull
= 370 cm/sec²
Average impact speed for:
Asteroid = 34km/sec
Comet = 87 km/sec
Size of Craters on Mercury
Simple craters on Mercury:
Range up to approx. 10 km in Diameter
(19 km on the Moon and 3 km on Earth)
Complex Craters:
Range from 10km up to 200km with a central peak
Range from about 200km to 750km with Double
Ring
Range from 750km to 1500 and up with multiple
rings.
The Largest Craters on
Mercury
The Caloris Basin is known to be the largest
crater basin in the Solar System.
Effects of the larger impacts are
as great as planetary change.
Antipodal changes in the surface
of the planet are a major side
effect of this large impact.
What These Craters Mean
for Scientists
By studying all effects of Mercury’s impact
history, we can discern eras of impacting,
possible sources of impacting, (i.e. asteroid
belts, comets, etc…), and ascertain the
historical records of Mercury through
observation, data collection and analysis.