100
votes
Accepted
Could the dinosaurs have seen the asteroid that killed them?
The answer is yes; for a few nights prior to the impact (assuming they had eyes with a similar sensitivity to our own and could look up!). It could be a bit longer than this if the body was larger ...
- 146k
41
votes
Why did they decide to hit Dimorphos in the retrograde direction rather than prograde; was it a "coin-toss" or were there implications for observing?
The original orbital period of Dimorphos was approximately 11.92 hours. The DART scientists weren't sure how much momentum was going to be exchanged due to the collision since they weren't sure how ...
- 16.2k
32
votes
How early could we detect an asteroid the size of the one that caused the extinction of the dinosaurs?
It could be as little notice as a few days.
There is a large variation in the amount of warning we would have before an asteroid strike similar in energy to Chicxulub. Let’s examine the case in which ...
- 16.2k
32
votes
Accepted
Is it possible that the Rosetta orbiter moved the comet when it crashed?
Yes, it did. But not by much.
The comet has a mass of about $10^{13}$ kg. Rosetta had a mass (after fuel had been used up) of about 1300kg. The "impact" was at 0.9 m/s. This means that ...
- 116k
31
votes
Accepted
Why are asteroids so much richer in precious metals than Earth's crust?
This is in part marketing hype by wanna-be asteroid mining companies. That said, some asteroids are suspected to be richer in precious metals than is the Earth's crust. For example, the Earth's crust ...
- 33.5k
29
votes
Accepted
Why was there a gap in the number of asteroid detections between 1807 and 1845?
Ceres, Pallas, Juno and Vesta were all discovered between 1801 and 1807. After that, astronomers looked in vain for 38 years until the 5th, Astraea was spotted on December 8, 1845 by German amateur ...
- 4,393
27
votes
Accepted
How fast would a one mile asteroid have to go for it to match the impact that killed the dinosaurs?
This is a nice little Fermi problem, and can be answered if we don't take it too seriously. The Chicxulub impact was 20km/s and about 10 kilometers in diameter (with a density of about 3g/cm³). Mass ...
- 116k
27
votes
How did asteroid (7482) 1994 PC1 get its "face"? Is it reconstructed from optical or radar imaging, or something else?
These are images taken from Nasa's Eyes on Asteroids site. It lets you see the orbit and get information about the asteroid in a nice interactive way. For asteroids with a known shape and surface ...
- 116k
26
votes
Where on Earth could dinosaurs feel the impact of their extinction asteroid?
The whole Earth "rippled" after the Chicxulub impact. By ripple, I specifically mean surface displacement. Current models indicate that it rippled enough that most of the dinosaurs and ...
- 16.2k
24
votes
Accepted
What caused this mysterious stellar occultation on July 10, 2017 from something ~100 km away from 486958 Arrokoth?
There were three attempts to measure Arrokoth by occultation, and the June 3rd attempt didn't detect anything. The July 10th attempt had a tiny blip, that appeared to be in the "wrong place"...
- 116k
22
votes
Accepted
Does anything orbit the Sun faster than Mercury?
The recently discovered asteroids 2019 LF6 and 2020 AV2, each taking 151 days to orbit the Sun, have the shortest periods currently listed in the JPL Small Body Database.
Vulcanoids are difficult to ...
- 18.2k
22
votes
Accepted
Did the temporary asteroid name DA₄₂ arise naturally and fortuitously (as a precursor to a Douglas Adams namesake)? Or did someone help it along?
There are other asteroids with provisional designation DA42.
"D" means the second half of February, A=1 and 42 means the letters A-Z (excluding J) have been assigned 42 times.
2001 DA42 ...
- 116k
22
votes
If the Earth had another moon would it be better protected from asteroids?
I don't quite buy JamesK's claim that "the moon only covers less than 0.001% of the sky, and so leaves us vulnerable to 99.999% of asteroids."
That argument would work if typical asteroids 1)...
- 2,506
21
votes
Accepted
Which kind of celestial body killed dinosaurs?
Definitions:
A meteoroid is a celestial object larger than an grain of dust and smaller than 1 meter in diameter.
An asteroid is a celestial object larger than 1 meter in diameter.
A meteor is a ...
- 7,439
20
votes
Accepted
Have we ever observed a body, such as a large asteroid, "hitting" the Sun?
Yes
and here's a video of "a Giant Comet Hitting the Sun":
https://www.youtube.com/watch?v=Mat4dWpszoQ
The impact occurred sometime during May 10-11, 2011. The comet was not named but believed to ...
- 356
20
votes
Gravitational Properties of Asteroids
Of course you would need to specify who the person is - an Olympic athlete? Let us assume so and then you can scale downwards accordingly.
So an Olympic high jumper can jump hard enough to raise ...
- 146k
20
votes
Accepted
If two asteroids will collide, how can we call it?
They are both called asteroids.
There is neither logic, nor science, nor even a convention of calling either body a "meteor", since meteors are strictly atmospheric phenomena, that occur ...
- 116k
19
votes
Was Theia a planet or an asteroid?
The IAU definition of "planet" is at best irrelevant here. The IAU defines a planet as a body that has cleared its neighbourhood. But in the early solar system the 8 bodies that are now ...
- 116k
18
votes
Has anyone back-calculated previous close encounters between the Apophis asteroid and Earth?
The JPL Small Body Database lists Apophis close approaches dating back 100 years before discovery.
Three fairly close ones were:
1907-04-13, 0.029 au
1949-04-14, 0.028 au
1990-04-14, 0.033 au
While ...
- 18.2k
18
votes
Accepted
What are the benefits of collecting asteroid samples in situ rather than just waiting for bits of asteroids to fall as meteorites?
This can be answered in two ways.
At the Earth's orbit we do not necessarily sample (meteoroid intercepting Earth and surviving atmospheric entry to fall as a meteorite) all the taxonomic types (...
- 811
17
votes
Accepted
Why did the distribution of asteroids discovered in 2010 have a radial modulation?
I'm pretty sure that the radial pattern found in the data is a result of WISE's approximately 90 minute sampling cadence (dictated by the satellite's orbit), astrometric precision (about 0.2 ...
- 2,946
17
votes
How early could we detect an asteroid the size of the one that caused the extinction of the dinosaurs?
There are two classes of object. One is "asteroids" and the other is "comets".
Asteroids orbit in fat ellipses, mostly between Mars and Jupiter, but some come closer and a few can ...
- 116k
17
votes
Accepted
Opportunities to see a near earth object via unaided eyes or binoculars?
Your best viewing opportunity will be 99942 Apophis which will pass Earth on April 13, 2029, where it will pass about 19,600 miles from Earth; look out for that. According to Wikipedia:
On that date, ...
- 6,613
17
votes
What if the Earth was hit by a small asteroid having close to the speed of light?
If the Earth was hit by an asteroid having diameter of about 5 km and moving with the speed close to the speed of light? What would happen?
According to https://what-if.xkcd.com/20/
The momentum ...
- 289
16
votes
Why do planets tend to rotate in the same direction although they have formed from tumbling asteroids?
You are right that the tilt of the asteroids are distributed in very random way, and that the rotation of the Solar nebula is a minor contributor to that tilt, and only skews it a little.
However, ...
16
votes
Accepted
What is the difference between the Yarkovsky effect and YORP effect?
The Yarkovsky effect is the thrust on a small object in space that has been heated by sunlight, created from radiant energy. The YORP effect is when the thrust produces rotation, likely due to uneven ...
- 2,616
16
votes
Accepted
Could this estimate of the size and mass of the Chicxulub Impactor be accurate?
Well, that article was never accepted for publication in any peer-review journal apparently.
That said, estimates may vary widely depending on assumptions about the composition and velocity of the ...
- 3,856
16
votes
Does anything orbit the Sun faster than Mercury?
There is a problem with very high velocity dust particles orbiting the Sun at distances much closer than Mercury with masses of micrograms and below. These particles can do damage to spacecraft that ...
- 31.4k
15
votes
Whats the probability of a hazardous impact for human life on Mars?
We actually have a very good idea of this because the Mars Reconnaissance Orbiter has been orbiting Mars for over a decade. The MRO is, basically, a spy satellite around Mars and is continually taking ...
- 7,580
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