35
votes
Is the science in "Don't Look Up" realistic?
Short observational arcs present difficulties in orbit determination. A couple of examples (taken from Wikipedia) :
(392741) 2012 SQ31 was observed for one day, and the best-fit orbit was found to ...
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30
votes
Is the science in "Don't Look Up" realistic?
Accurate determination of collision within 1 day of discovery is realistic only if old pre-discovery measurement data is available.
We can approximate the orbit determination accuracy with some ...
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20
votes
Could an object enter or leave the vicinity of the Earth without being detected?
The Chelyabinsk meteor exploded over Chelyabinsk Oblast just shy of a decade ago. It was estimated after the fact to have been about 20 meters in diameter. No organization saw it before it entered the ...
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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, ...
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11
votes
Accepted
Could 99942 Apophis break up due to Earth's gravity during 2029 flyby?
Unlikely.
An asteroid can break up due to tidal forces if it approaches a planet closer than the Roche limit. The exact size of the Roche limit depends on the density of the object and whether it is ...
- 129k
8
votes
Accepted
Is there a distinction between NEOs and near-Earth asteroids? Is there a difference?
Yes, Near Earth Objects (NEOs) include asteroids (Near Earth Asteroids (NEAs)) and a few percent of comets (Near Earth Comets (NECs)). As shown by the Update to Determine the Feasibility of Enhancing ...
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7
votes
Can Earth have a ring?
Most planets don't have rings. The ring region is inside the Roche limit which is quite close to the planet. A ring system outside the Roche limit needs to be either very faint or, it would over ...
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7
votes
Accepted
Basics of Tracklet-less Heliocentric Orbit Recovery (THOR) - simple breakdown of how it works?
Thanks for your question and your interest in the THOR algorithm. THOR is the product of my PhD dissertation so I figured I’d take a stab at answering your question. It’s super humbling and inspiring ...
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7
votes
Accepted
What would happen to a mile-wide sphere of water ice that slammed into the Earth at 90 degrees straight down, at 35,000 MPH?
Your "it would smash into the earth just like any other asteroid" intuition is basically correct. This hypothetical comet would have less mass than an asteroid of the same size (because ice ...
- 18.4k
6
votes
Newtons law of Gravitation
For gravity the force is :
$$F=\frac {G M_1 M_2} {r^2}$$
But the acceleration :
$$a=\frac F {M_2} =\frac {G M_1 } {r^2}$$
and this is the same for all bodies as it depends only on the primary's ...
- 6,401
6
votes
Accepted
Has Hubble ever been used to try to image a near Earth asteroid?
[rewritten to address the revised question]
Maybe, depending on how fussy you want to be about "resolved".
This is a study from 1995, using observations of asteroid 4179 Toutatis made in 1992 with ...
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5
votes
Accepted
How poor was our tally of objects that could produce potential extinction-level events back in 1998?
It was fairly poor. Wikipedia has a list of large, potentially hazardous asteroids, and 9 on that list were known before 1998:
2201 Olijato
1620 Geographos
4183 Cuno
1981 Midas
3122 Florence
3200 ...
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5
votes
Accepted
Has a near earth object in heliocentric orbit ever been bright enough to be visible to the unaided eye?
The Near-Earth close approches website shows close approaches to the Earth by near-Earth objects (NEOs). The table showing all close encounters indicates the absolute magnitude.
The data can be ...
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5
votes
Accepted
Fastest recorded apparent motion of a comet or asteroid seen from Earth (degrees/day)?
This is more of a recent example than a record.
On 2019-07-25, asteroid 2019 OK passed about 65000 km from the Earth at a relative speed of 24.5 km/s.
The Minor Planet Center lists multiple
...
- 18.8k
5
votes
Accepted
Reference frames in relativity?
It depends on your definition of "layman" but Patrick Wallace has a slide presentation on what changed and why with the new reference systems. There is also the USNO Circular 179 which covers all of ...
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5
votes
Accepted
2001 VB - when will it be reacquired?
The remote chance of an Earth impact in late July 2023 may depend on hitting a small "keyhole" near Venus on 2002-01-09.
NEODyS gives an 8% chance that 2001 VB even passed within 0.1 au of ...
- 18.8k
5
votes
Could an object enter or leave the vicinity of the Earth without being detected?
Each year, several small NEOs pass Earth closer than the distance of the Moon. Here is the list of NEOs that has been detected recently but still, many of them passes through undetected. The main ...
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4
votes
Will 1036 Ganymed's orbit be changed by its close encounter with Mars in 2176?
Ganymed's Mars approach in 2176 is only moderately close: 4.4 times Mars's Hill sphere radius or 11 times the average Earth-Moon distance.
JPL HORIZONS predicts these heliocentric orbital elements (...
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4
votes
Accepted
How was a rock on the surface of asteroid 101955 Bennu first observed from Earth (Benben Saxum)?
I think it is the "boulder" discovered by Nolan et al. (2013). They used radar images from two ground-based observatories, from two different passes, to perform shape modeling:
The radar ...
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4
votes
Accepted
With only seemingly two measurements 30 minutes apart, how were astronomers able to determine that asteroid 2022 EB5's trajectory intersected Earth?
The object was already so close to the Earth that in the 30 min time difference between the observations it moved already 1/4 of the way further to the earth (from about 21 Earth radii distance to 16 ...
- 3,611
4
votes
Appropriate NEO databases for preliminary orbit determination simulations
The Minor Planet Center (MPC) is the officially designated clearing house for all asteroid observations, including Near-Earth Objects (NEOs). Their database has the records of all observations for all ...
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4
votes
Will Webb observe a sample of the outer solar system to estimate the population of objects that might endanger Earth?
It does. As a complementary science.
While JWST observes galaxies and stars far far away, small bodies of Solar System are a "foreground noise". The closest asteroids to Earth can be moving ...
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3
votes
Which solar system objects have the least stable solar orbits?
The least stable orbits are likely the temporarily captured orbiters of Earth and other planets. These are bodies that have been captured by the Earth/Moon gravity well and move from solar orbits to ...
- 129k
3
votes
Accepted
Retrogradation movement of planet Mars relatively from Earth by Copernic
You are right. If Mars orbited in exactly the same plane as the Earth, instead of an S or a loop, we would see Mars moving prograde relative for the stars along the ecliptic, then slowing and ...
- 129k
3
votes
Accepted
Size and Mass of a typical "small" asteroid that impacts the Earth?
For the asteroid not to break up it needs to either be big, or tough.
You can experiment with the impact effects calculator but you should notice that a rocky asteroid with a diameter of less than ...
- 129k
3
votes
Accepted
Discovery of Near Earth Objects (NEO's)
This is because there are many more small NEOs than there are large ones and the larger ones are easier to find and so were found first. The numbers of NEOs follow what's know as a power law ...
- 8,792
3
votes
Why is the difference between Apollo and Aten asteroids considered meaningful?
The first point to make is that categorization isn't an exact science. It's done for convenience and practicality and sometimes, familiarity. It's not going to be perfect.
The second point to make ...
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3
votes
How would a small TCO (temporarily captured orbiter) or other natural Earth satellite most likely be detected?
Cruithne and J002E3 were detected using ground based astrophotography.
J002E3 is thought to be "the S-IVB third stage of the Apollo 12 Saturn V rocket ... It is thought that J002E3 left Earth orbit in ...
- 4,548
3
votes
Accepted
What would people on Earth see during a close comet pass?
Hear and smell: Nothing. The comet and its coma are well outside the atmosphere, no sound or scent can travel through space.
The coma of the comet could be 30000km across, bigger than the moon, and ...
- 129k
2
votes
Would a comet break up during a close pass of the Earth
No, that isn't close enough. The Roche Limit for break up of a rigid body, caused by tidal forces is given by
$$d = 1.26 R_C \left(\frac{M_E}{M_C}\right)^{1/3},$$
where $M_E$ is the mass of the Earth, ...
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