An asteroid collision big enough and fast enough to see a massive ejection of rock and moon-chunks, from the surface of the earth AND not wipe out the population of the planet.
What size and speed of asteroid would it take to have a majorly visible and spectacular impact on the moon?
What after effects would this have? What would the moon look like? Would there be any minor effects in the earth?
Something the size of the Chicxulub impactor would be plenty spectacular - the top range of its impact energy is fifty thousand gigatons of TNT equivalent. There wouldn't be an equivalent explosion in all of human existence.
The major problem is that in order to save humanity from an impact, by definition any impactor would have to hit the far side of the moon. The ejecta would be visible, as would the motion of the moon itself, but not the moment of impact.
Any impact sufficient to be visible on the near side - ie. force projected through the entire moon, possibly destroying it - will give you the same problem experienced by the human race in Neal Stephenson's Seveneves: a hard rain.
For added fun, I adapted a python script I found here:
import matplotlib.pyplot as plt
import math
plt.ion()
G = 6.673e-11 # gravitational constant
gridArea = [-20, 50, -20, 50] # margins of the coordinate grid
gridScale = 10000000 # 1 unit of grid equals 10000000m or 10000km
plt.clf() # clear plot area
plt.axis(gridArea) # create new coordinate grid
plt.grid(b="on") # place grid
class Object:
_instances = []
def __init__(self, name, position, radius, mass):
self.name = name
self.position = position
self.radius = radius # in grid values
self.mass = mass
self.placeObject()
self.velocity = 0
Object._instances.append(self)
def placeObject(self):
drawObject = plt.Circle(self.position, radius=self.radius, fill=False, color="black")
plt.gca().add_patch(drawObject)
plt.show()
def giveMotion(self, deltaV, motionDirection, time):
if self.velocity != 0:
x_comp = math.sin(math.radians(self.motionDirection))*self.velocity
y_comp = math.cos(math.radians(self.motionDirection))*self.velocity
x_comp += math.sin(math.radians(motionDirection))*deltaV
y_comp += math.cos(math.radians(motionDirection))*deltaV
self.velocity = math.sqrt((x_comp**2)+(y_comp**2))
if x_comp > 0 and y_comp > 0: # calculate degrees depending on the coordinate quadrant
self.motionDirection = math.degrees(math.asin(abs(x_comp)/self.velocity)) # update motion direction
elif x_comp > 0 and y_comp < 0:
self.motionDirection = math.degrees(math.asin(abs(y_comp)/self.velocity)) + 90
elif x_comp < 0 and y_comp < 0:
self.motionDirection = math.degrees(math.asin(abs(x_comp)/self.velocity)) + 180
else:
self.motionDirection = math.degrees(math.asin(abs(y_comp)/self.velocity)) + 270
else:
self.velocity = self.velocity + deltaV # in m/s
self.motionDirection = motionDirection # degrees
self.time = time # in seconds
self.vectorUpdate()
def vectorUpdate(self):
self.placeObject()
data = []
for t in range(self.time):
motionForce = self.mass * self.velocity # F = m * v
x_net = 0
y_net = 0
for x in [y for y in Object._instances if y is not self]:
distance = math.sqrt(((self.position[0]-x.position[0])**2) +
(self.position[1]-x.position[1])**2)
gravityForce = G*(self.mass * x.mass)/((distance*gridScale)**2)
x_pos = self.position[0] - x.position[0]
y_pos = self.position[1] - x.position[1]
if x_pos <= 0 and y_pos > 0: # calculate degrees depending on the coordinate quadrant
gravityDirection = math.degrees(math.asin(abs(y_pos)/distance))+90
elif x_pos > 0 and y_pos >= 0:
gravityDirection = math.degrees(math.asin(abs(x_pos)/distance))+180
elif x_pos >= 0 and y_pos < 0:
gravityDirection = math.degrees(math.asin(abs(y_pos)/distance))+270
else:
gravityDirection = math.degrees(math.asin(abs(x_pos)/distance))
x_gF = gravityForce * math.sin(math.radians(gravityDirection)) # x component of vector
y_gF = gravityForce * math.cos(math.radians(gravityDirection)) # y component of vector
x_net += x_gF
y_net += y_gF
x_mF = motionForce * math.sin(math.radians(self.motionDirection))
y_mF = motionForce * math.cos(math.radians(self.motionDirection))
x_net += x_mF
y_net += y_mF
netForce = math.sqrt((x_net**2)+(y_net**2))
if x_net > 0 and y_net > 0: # calculate degrees depending on the coordinate quadrant
self.motionDirection = math.degrees(math.asin(abs(x_net)/netForce)) # update motion direction
elif x_net > 0 and y_net < 0:
self.motionDirection = math.degrees(math.asin(abs(y_net)/netForce)) + 90
elif x_net < 0 and y_net < 0:
self.motionDirection = math.degrees(math.asin(abs(x_net)/netForce)) + 180
else:
self.motionDirection = math.degrees(math.asin(abs(y_net)/netForce)) + 270
self.velocity = netForce/self.mass # update velocity
traveled = self.velocity/gridScale # grid distance traveled per 1 sec
self.position = (self.position[0] + math.sin(math.radians(self.motionDirection))*traveled,
self.position[1] + math.cos(math.radians(self.motionDirection))*traveled) # update pos
data.append([self.position[0], self.position[1]])
collision = 0
for x in [y for y in Object._instances if y is not self]:
if (self.position[0] - x.position[0])**2 + (self.position[1] - x.position[1])**2 <= x.radius**2:
collision = 1
impactor = self.name
impactee = x.name
velocity = self.velocity
break
if collision != 0:
print("Collision! %s struck %s at %d m/s" % (impactor, impactee, velocity))
break
plt.plot([x[0] for x in data], [x[1] for x in data])
Earth = Object(name="Earth", position=(0.0, 25.0), radius=0.6371, mass=5.972e24)
Moon = Object(name="Moon", position=(38.45, 25.0), radius=0.1737, mass = 7.347e22) # The orbital distance of the moon is ~ 384.5 thousand km.
Hammer = Object(name="Hammer", position=(38.80, 25.20), radius=0.0001, mass=1.0e10)
Hammer.giveMotion(deltaV=2000.0, motionDirection=270, time=100000)
plt.show(block=True)
The Hammer is just 10Mkg, but its mass is always going to be somewhat irrelevant.
I can think of ways the impact could be visible from Earth.
1 Possibly the impact would create a cloud of dust particles and vaporized rock that would expand to several times the diameter of the moon and be lit from below by red hot or hotter lava created by the impact and easily visible from Earth
2 Possibly the asteroid is headed directly for Earth but passes close to the Moon and the lunar gravity bends the course of the asteroid toward the moon a little. The asteroid thus barely misses the Earth and whips around it and is slung back toward the Moon. The asteroid hits the moon on the near side in a tremendous explosion. And astronomers calculate that if the asteroid hadn't hit the Moon it would eventually have fallnd back on Earth causing an extinction event.
If you use one of those suggestions try to calculate if it is possible with the gravitional forces and the probable asteroid velocity range.
