<p>Any prediction for 2001 VB depends on a small set of observations spanning 7 days in November 2001.
JPL <a href="https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2001%20VB" rel="nofollow noreferrer">SBDB</a> estimates its orbital period as 1351±124 days, uncertain by 9%.
It may be useful to think of its probable position as a cloud instead of a point.
If I read the vector tables from JPL <a href="https://ssd.jpl.nasa.gov/horizons/app.html#/" rel="nofollow noreferrer">HORIZONS</a> correctly,
that cloud has grown from 30 by 3×10<sup>5</sup> km when it was observed,
to 10<sup>5</sup> by 3×10<sup>6</sup> km 4 months later when it was supposed to have encountered Venus,
to 3×10<sup>6</sup> by 6×10<sup>8</sup> km now.</p>
<p><a href="https://web.archive.org/web/20230706183152/https://neo.ssa.esa.int/risk-list" rel="nofollow noreferrer">ESA's risk list</a> has different rules for inclusion than <a href="https://cneos.jpl.nasa.gov/sentry/" rel="nofollow noreferrer">JPL Sentry</a> does, but they computed similar orbital parameters and uncertainties from the same set of observations.
On the &quot;Orbit Properties&quot; tab <a href="https://web.archive.org/web/20230330235645/https://neo.ssa.esa.int/search-for-asteroids?sum=1&amp;des=2001VB" rel="nofollow noreferrer">here</a>, their estimate for <a href="https://en.wikipedia.org/wiki/Mean_anomaly" rel="nofollow noreferrer">mean anomaly</a> at MJD 60000 (2023-02-25) has a ±168° error bar.
In other words, for all we know, 2001 VB could now be almost anywhere along its orbit.</p>
<p>All bets are off. Only a new observation can change this, and unfortunately none is available.</p>

CC BY-SA 4.0
2023-07-23T17:09:03.610Z
2023-07-24T14:59:00.233Z
2023-07-24T14:59:00.233Z
Mike G
<p>It's not on JPL but for some reason it's on ESA. Though for the ESA it states its next approach isn't until 2048. It at one point had a chance, but the chance only ever got to 1 in 200 million. It was scratched off the sentry risk list in early 2021, which means it cites no danger to earth. And both observation sites pin the asteroid either ~2.7 or ~3.2 au away from earth as of July 22nd 2023.</p>

CC BY-SA 4.0
2023-07-24T20:31:46.937Z
Given the extremely wide range of possible positions *now*, I'm not sure how ESA can establish even a year for the next approach. Sounds like guesswork to me.
Darth Pseudonym
CC BY-SA 4.0
2023-07-23T00:02:13.973Z
2023-07-24T14:59:55.113Z
2023-07-24T14:59:55.113Z
Andyhasaquestion
<p>Why is asteroid 2001VB still on the risk list and how likely is it to impact the Earth this year? Moreover, on July 23, 2023 it will be several kilometers from us according to NASA's orbit view, how can it impact?</p>

CC BY-SA 4.0
2023-06-08T07:03:13.733Z
"Several kilometers" is **very close**. Did you mean a larger number such a several thousand kilometers?
Fred
CC BY-SA 4.0
2023-06-08T07:06:29.017Z
Does this answer your question: [2001 VB - when will it be reacquired?](https://astronomy.stackexchange.com/questions/44497/2001-vb-when-will-it-be-reacquired)?
Fred
CC BY-SA 4.0
2023-06-08T07:25:26.707Z
yes, I meant that.
But if the probability that it impacts was for a “keyhole” in the Venus flyby in 2002, at 0.1 AU. According to their calculations it passed at a distance of 0.02 AU, the impact should be almost certain or not?
Elena Targetti
CC BY-SA 4.0
2023-06-08T07:49:19.607Z
1AU = 150 million kilometers = distance Sun-Earth. Thus 0.02 AU = 3 million kilometers or of the order of 300 Earth diameter or 10 distances moon-earth
planetmaker
CC BY-SA 4.0
2023-06-08T14:34:26.963Z
this doesn't answer my question…
Elena Targetti
CC BY-SA 4.0
2023-06-08T14:47:08.337Z
See https://cneos.jpl.nasa.gov/sentry/intro.html for info on how impact risk is determined, including the new algorithm which was introduced in 2021.
PM 2Ring
CC BY-SA 4.0
2023-06-08T20:08:08.373Z
This object isn't on the risk list.
James K
CC BY-SA 4.0
2023-06-09T09:51:26.070Z
@JamesK it looks like its at the top of this list: https://neo.ssa.esa.int/risk-list
GrapefruitIsAwesome
CC BY-SA 4.0
2023-06-09T17:01:08.147Z
that's right, this is number one on the list. So is the probability of impact up to date or is it based on the 2001 calculations?
And considering that it passed within 0.1 AU of Venus in 2002, has the probability changed?
Elena Targetti
CC BY-SA 4.0
2023-06-09T18:33:29.643Z
See https://cneos.jpl.nasa.gov/sentry/details.html#?des=2001%20VB
James K
CC BY-SA 4.0
2023-06-13T06:44:08.430Z
which is the correct one?
Elena Targetti
<observational-astronomy>
Why is asteroid 2001VB still on the risk list?
Elena Targetti
# Why is asteroid 2001VB still on the risk list?

(Asked by: username_0 on 2023-06-08)

Why is asteroid 2001VB still on the risk list and how likely is it to impact the Earth this year? Moreover, on July 23, 2023 it will be several kilometers from us according to NASA's orbit view, how can it impact?

**Tags:** observational-astronomy
> **Comments:**
> **username_1**: "Several kilometers" is **very close**. Did you mean a larger number such a several thousand kilometers?  
> **username_1**: Does this answer your question: [2001 VB - when will it be reacquired?](https://astronomy.stackexchange.com/questions/44497/2001-vb-when-will-it-be-reacquired)?  
> **username_0**: yes, I meant that. But if the probability that it impacts was for a “keyhole” in the Venus flyby in 2002, at 0.1 AU. According to their calculations it passed at a distance of 0.02 AU, the impact should be almost certain or not?  
> **username_2**: 1AU = 150 million kilometers = distance Sun-Earth. Thus 0.02 AU = 3 million kilometers or of the order of 300 Earth diameter or 10 distances moon-earth  
> **username_0**: this doesn't answer my question…  
> **username_3**: See https://cneos.jpl.nasa.gov/sentry/intro.html for info on how impact risk is determined, including the new algorithm which was introduced in 2021.  
> **username_4**: This object isn't on the risk list.  
> **username_5**: @JamesK it looks like its at the top of this list: https://neo.ssa.esa.int/risk-list  
> **username_0**: that's right, this is number one on the list. So is the probability of impact up to date or is it based on the 2001 calculations? And considering that it passed within 0.1 AU of Venus in 2002, has the probability changed?  
> **username_4**: See https://cneos.jpl.nasa.gov/sentry/details.html#?des=2001%20VB  
> **username_0**: which is the correct one?  

---

## 2 answers

### Answer by username_6 on 2023-07-23. Score: 1

Any prediction for 2001 VB depends on a small set of observations spanning 7 days in November 2001.
JPL [SBDB](https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2001%20VB) estimates its orbital period as 1351±124 days, uncertain by 9%.
It may be useful to think of its probable position as a cloud instead of a point.
If I read the vector tables from JPL [HORIZONS](https://ssd.jpl.nasa.gov/horizons/app.html#/) correctly,
that cloud has grown from 30 by 3×105 km when it was observed,
to 105 by 3×106 km 4 months later when it was supposed to have encountered Venus,
to 3×106 by 6×108 km now.

[ESA's risk list](https://web.archive.org/web/20230706183152/https://neo.ssa.esa.int/risk-list) has different rules for inclusion than [JPL Sentry](https://cneos.jpl.nasa.gov/sentry/) does, but they computed similar orbital parameters and uncertainties from the same set of observations.
On the "Orbit Properties" tab [here](https://web.archive.org/web/20230330235645/https://neo.ssa.esa.int/search-for-asteroids?sum=1&des=2001VB), their estimate for [mean anomaly](https://en.wikipedia.org/wiki/Mean_anomaly) at MJD 60000 (2023-02-25) has a ±168° error bar.
In other words, for all we know, 2001 VB could now be almost anywhere along its orbit.

All bets are off. Only a new observation can change this, and unfortunately none is available.


---

### Answer by username_7 on 2023-07-23. Score: 0

It's not on JPL but for some reason it's on ESA. Though for the ESA it states its next approach isn't until 2048. It at one point had a chance, but the chance only ever got to 1 in 200 million. It was scratched off the sentry risk list in early 2021, which means it cites no danger to earth. And both observation sites pin the asteroid either ~2.7 or ~3.2 au away from earth as of July 22nd 2023.

> **Comments:**
> **username_8**: Given the extremely wide range of possible positions *now*, I'm not sure how ESA can establish even a year for the next approach. Sounds like guesswork to me.  

---

