<p>Unlikely.</p>
<p>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 likely to deform fluidly under tidal stress.</p>
<p>We don't know the physical nature of Apopsis, but if we assume it is a very weakly held-together rubble pile, with a low density, then the Roche limit is still about 20,000 km.  That is a lot less than the 40,000 km distance that it is predicted to pass. And since interest in this object has (naturally) been so great, its orbit is very well understood, the closest approach distance is now determined to be <a href="https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&amp;COMMAND=%27Apophis%27&amp;START_TIME=%272029-Apr-13%2021:46%27&amp;STOP_TIME=%272029-Apr-14%27&amp;STEP_SIZE=%272%20days%27&amp;QUANTITIES=%2720,39%27" rel="noreferrer">38016 km</a> to within 3.4 km.</p>
<p>The asteroid will also only stay in Earth's vicinity for a short period of time. There isn't much time for it to deform fluidly, and so it may behave more like a solid (on this time scale) which would make break up less likely.  For tidal forces to be strong enough to cause it to split up, one would have to assume it had a density comparable to polystyrene.</p>
<p>Your article describes what is likely:  slow rock slides of unconsolidated material.  This is a long way from a dramatic event like splitting.</p>

CC BY-SA 4.0
2023-09-25T19:11:33.100Z
Some work on tidal resurfacing on Apophis were presented at the 'Apophis T-7 meeting' from 2022. The program and the 2 page abstracts are available from meeting's [program page](https://www.hou.usra.edu/meetings/apophis2022/pdf/apophis2022_program.htm); Session 2 dealt with "Possible Consequences on Apophis For Earth's Torques or Tidal Stress"
astrosnapper
CC BY-SA 4.0
2023-09-26T07:08:10.297Z
One talk title might summarize the expected effect quite well: "Modeling Tidally-Induced Resurfacing on 99942 Apophis During its 2029 Close Encounter with Earth [#2024]
Simulations investigating the **motion of surface grains** due to Earth tides on Apophis. Our results may be important for indicating potential albedo changes or identifying regions of interest for surface grain motion for in-situ missions." (emphasis mine)
planetmaker
CC BY-SA 4.0
2023-09-25T18:20:04.303Z
2023-09-26T02:13:15.637Z
2023-09-26T02:13:15.637Z
James K
<p>Asteroid <a href="https://en.wikipedia.org/wiki/99942_Apophis#Orbit" rel="noreferrer">99942 Apophis</a> is due to pass close to the Earth in 2029, at a distance of slightly less than 40,000 Kilometres. According to the description we have, the shape is irregular and elongated. It is probably formed by several objects loosely held together by a small gravity. So I wondered if those features make it so fragile that it might break up under the pull of Earth's gravity.</p>
<p>I searched the question on the internet and I found only an <a href="https://phys.org/news/2014-10-asteroid-apophis-landslides-earth.html" rel="noreferrer">article</a> that says that the Earth's gravity during the flyby could cause some landslides. But the authors say that the study didn't have very precise data, they had to take some assumptions.</p>
<p>Beside that article I did not find anything else. With a slight change of the assumption could the asteroid break up during the flyby?</p>

CC BY-SA 4.0
2023-09-25T21:29:55.220Z
The current Horizons trajectory has a solution date of 2021-Jun-29. The close approach is ~2029-Apr-13 21:45 UT, at a distance of ~ 38011.4 km https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&CSV_FORMAT=YES&OBJ_DATA=NO&VEC_TABLE=6&COMMAND=99942&CENTER=%40399&START_TIME=%272029-Apr-13+15%3A45+UT%27&STOP_TIME=%272029-Apr-14+3%3A45%27&STEP_SIZE=15m
PM 2Ring
CC BY-SA 4.0
2023-09-25T21:53:46.220Z
It doesn't spend much time near Earth, but it does get visibly deflected. (You can plot its trajectory in 3D with my script at the end of https://astronomy.stackexchange.com/a/49823/16685 Its ID is 99942).
PM 2Ring
<near-earth-object>
Could 99942 Apophis break up due to Earth's gravity during 2029 flyby?
FluidCode
# Could 99942 Apophis break up due to Earth's gravity during 2029 flyby?

(Asked by: username_0 on 2023-09-25)

Asteroid [99942 Apophis](https://en.wikipedia.org/wiki/99942_Apophis#Orbit) is due to pass close to the Earth in 2029, at a distance of slightly less than 40,000 Kilometres. According to the description we have, the shape is irregular and elongated. It is probably formed by several objects loosely held together by a small gravity. So I wondered if those features make it so fragile that it might break up under the pull of Earth's gravity.

I searched the question on the internet and I found only an [article](https://phys.org/news/2014-10-asteroid-apophis-landslides-earth.html) that says that the Earth's gravity during the flyby could cause some landslides. But the authors say that the study didn't have very precise data, they had to take some assumptions.

Beside that article I did not find anything else. With a slight change of the assumption could the asteroid break up during the flyby?

**Tags:** near-earth-object
> **Comments:**
> **username_1**: The current Horizons trajectory has a solution date of 2021-Jun-29. The close approach is ~2029-Apr-13 21:45 UT, at a distance of ~ 38011.4 km https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&CSV_FORMAT=YES&OBJ_DATA=NO&VEC_TABLE=6&COMMAND=99942&CENTER=%40399&START_TIME=%272029-Apr-13+15%3A45+UT%27&STOP_TIME=%272029-Apr-14+3%3A45%27&STEP_SIZE=15m  
> **username_1**: It doesn't spend much time near Earth, but it does get visibly deflected. (You can plot its trajectory in 3D with my script at the end of https://astronomy.stackexchange.com/a/49823/16685 Its ID is 99942).  

---

## 1 answers

### Answer by username_2 on 2023-09-25. Score: 11 | Accepted answer

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 likely to deform fluidly under tidal stress.

We don't know the physical nature of Apopsis, but if we assume it is a very weakly held-together rubble pile, with a low density, then the Roche limit is still about 20,000 km. That is a lot less than the 40,000 km distance that it is predicted to pass. And since interest in this object has (naturally) been so great, its orbit is very well understood, the closest approach distance is now determined to be [38016 km](https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Apophis%27&START_TIME=%272029-Apr-13%2021:46%27&STOP_TIME=%272029-Apr-14%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27) to within 3.4 km.

The asteroid will also only stay in Earth's vicinity for a short period of time. There isn't much time for it to deform fluidly, and so it may behave more like a solid (on this time scale) which would make break up less likely. For tidal forces to be strong enough to cause it to split up, one would have to assume it had a density comparable to polystyrene.

Your article describes what is likely: slow rock slides of unconsolidated material. This is a long way from a dramatic event like splitting.

> **Comments:**
> **username_3**: Some work on tidal resurfacing on Apophis were presented at the 'Apophis T-7 meeting' from 2022. The program and the 2 page abstracts are available from meeting's [program page](https://www.hou.usra.edu/meetings/apophis2022/pdf/apophis2022_program.htm); Session 2 dealt with "Possible Consequences on Apophis For Earth's Torques or Tidal Stress"  
> **username_4**: One talk title might summarize the expected effect quite well: "Modeling Tidally-Induced Resurfacing on 99942 Apophis During its 2029 Close Encounter with Earth [#2024] Simulations investigating the **motion of surface grains** due to Earth tides on Apophis. Our results may be important for indicating potential albedo changes or identifying regions of interest for surface grain motion for in-situ missions." (emphasis mine)  

---

