Back at the VATT, an Update: Protecting the Earth from The Big One, 120 Asteroids and Counting
In my previous article, Observing at the VATT, Part 4a, I gave some background on Mount Graham and what a typical trip to the mountain is like.
In this article, I will talk about the results of our program on the Vatican Advanced Technology Telescope, the VATT, and on our most recent observations. First, I would like to give a shout out to my team. I have been fortunate enough to observe with Mark Trueblood and Robert Crawford who, while not professional astronomers, bring the skills that have made our observing program on the VATT a success. We started working together in 2008. Mark and Robert have the engineering and computer skills that are critical to our program, and they are experienced observers. I am the Small Solar System Bodies expert. I have included short biographies of Mark and Robert below. Both Mark and Robert have also made significant contributions to the VATT as it transitions to a fully automated telescope.
For seven years, we had observing access to several different telescopes on Kitt Peak in southwest Arizona. Unfortunately, those telescopes became dedicated to other programs and fortunately, at about the same time, we were able to get access to the VATT. While the VATT is a smaller telescope (1.8 m vs. 2.1m and 2.3 m), Mt. Graham is a higher and darker site than Kitt Peak (1,200 meters [4,000 ft] higher), so a much better observing site (when it is clear).
Some Background
Asteroid Sample Return Missions
Asteroid 25143 Itokawa (named after Hideo Itokawa, the father of Japanese rocketry) was visited by the Japanese Space Agency’s (JAXA) Hayabusa (“Peregrine Falcon”) spacecraft. This was the first asteroid sample return mission. The spacecraft arrived in 2005, retrieved a surface sample soon after, and returned that sample to Earth in 2010. Itokawa has a mean diameter of about 315 meters and appears to be what is called a contact binary asteroid.
From the Editor: Check out the video at the bottom by Scott Manley – “The Crazy Story Of Japan’s First Asteroid Mission.” Hayabusa had to overcome massive technical problems to return its sample to Earth.
Image 1: Near-Earth Asteroid (and Potentially Hazardous Object) 25143 Itokawa
Asteroid 162173 Ryugu (“Dragon Palace”) was visited from 2018 to 2019 by the by the Japanese Space Agency’s (JAXA) Hayabusa2 (“Peregrine Falcon 2”) spacecraft. Asteroid 101955 Bennu (the Egyptian mythological bird associated with the Sun, creation, and rebirth) was visited by NASA’s OSIRIS-REx spacecraft (Osiris, the Egyptian god of fertility, agriculture, the afterlife, the dead, resurrection, life, and vegetation) from the end of 2018 to 2021.
Image 2: Two Near-Earth Asteroids that were the targets of two sample return missions. Both asteroids are also Potentially Hazardous Objects (see Part 1).
Planetary Defense
The Near-Earth Asteroid/Potentially Hazardous Object 65803 Didymos and its satellite Dimorphos were the target of NASA’s Double Asteroid Redirection Test (DART) mission in November of 2021.
Video: NASA’s DART mission impact with Near-Earth Asteroid/Potentially Hazardous Object 65803 Didymos’ satellite, Dimorphos.
From the Editor: Click here to see an interactive simulation of NASA’s DART mission impact in NASA’s Eyes on the Solar System web app.
Also, on July 4, 2005, comet 103/P Hartley 2 was hit by an impactor released from NASA’s Deep Impact mission. While not technically a planetary defense mission, it did prove the ability to intercept a comet.
Near-Earth Objects and Potentially Hazardous Objects
Image 3: Near-Earth Asteroid (and Potentially Hazardous Object) 4179 Toutatis (a Celtic god). The Chinese spacecraft Chang’e 2 (an ancient Chinese moon goddess) orbited Earth’s Moon from 2010 to 2011. After that, it left lunar orbit and flew by Toutatis in 2012. Toutatis has a mean diameter of 2.5 kilometers and appears to be what is called a contact binary asteroid.
Here are some important definitions from NASA/JPL’s Center for Near-Earth Object Studies:
- In terms of orbital elements, NEOs are asteroids and comets with perihelion [closest distance to the Sun] distance less than 1.3 AU [1 AU, an Astronomical Unit, is the mean distance of the Earth from the Sun]. Near-Earth Comets (NECs) are further restricted to include only short-period comets (i.e., orbital period P less than 200 years). The vast majority of NEOs are asteroids, referred to as Near-Earth Asteroids (NEAs). NEAs are divided into groups (Atira, Aten, Apollo, and Amor) according to their perihelion distance (q), aphelion [farthest distance from the Sun] distance (Q), and their semi-major axes (a).
- Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroid’s potential to make threatening close approaches to the Earth. Specifically, all asteroids with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 AU or less [19.5 times the distance to the Moon] and an absolute magnitude (H) of 22.0 or less are considered PHAs. In other words, asteroids that can’t get any closer to the Earth (i.e., MOID) than 0.05 AU (roughly 7,480,000 km or 4,650,000 mi) or are smaller than about 140 m (~500 ft) in diameter (i.e., H = 22.0 with assumed albedo of 14%) are not considered PHAs.
The terms NEO and PHO are preferred to NEA and PHA, as with minimal information, you do not know if an object is an asteroid or an extinct comet (or at least one that has no detectable coma). It is estimated that as many as 10% of NEOs may be extinct comets.
Image 4: Cumulative number of known Near-Earth Asteroids (NEAs) versus time. Credit: JPL
As of October 22, 2025, there were 877 known NEOs larger than a kilometer, 11,459 known NEOs larger than 140 meters, and a total of 39,849 known NEOs. Of these, 2,490 are classified as PHOs. In any given month 100 to 150 asteroids will be discovered that come within 0.05 AU (19.5 times the distance to the Moon). In addition, there are 1,846 NEOs on the ESA’s Risk List that have a non-zero impact probability, usually due to the uncertainty of their orbital parameters.
Presently most of the big surveys are in the Northern Hemisphere, so more are discovered in the northern winter when the nights are longer (and the weather is better). Ten or so of these will come closer than the distance to the Moon. Ten or so will be asteroids that have been observed in previous close approaches to the Earth. Their sizes usually range from about a meter up to 500 meters or more in diameter (about 3 to 1,500 feet). Things will change when the Vera C. Rubin Observatory in Chile comes online. The telescope itself is called the Simonyi Survey Telescope.
The telescope is expected to discover more than 10,000 NEOs a month! Many of these will be too faint for most amateur telescopes, so having a larger telescope such as the VATT will be important for follow-up observations of these NEOs.
Image 5: This diagram shows the orbits of 2,200 potentially hazardous objects as calculated by JPL’s Center for Near Earth Object Studies (CNEOS). Highlighted is the orbit of the asteroid 65803 Didymos and its moon Dimorphos, the target of NASA’s DART mission. Credit: NASA/JPL-Caltech
From the Editor: Click here to see an interactive simulation of asteroids in our solar system in NASA’s Eyes on Asteroids web app.
As I said in my previous articles about observing at the VATT, our goal is to observe NEOs that might, sometime in the future, collide with the Earth. These asteroids might become lost because of the uncertainty in their orbits. By reducing the uncertainty in the orbits of these asteroids, we hope to remove them from the list of potential asteroid impactors and improve their orbits to facilitate future recoveries of these asteroids. It may be years before they are close enough to the Earth for them to be observable again.
In the last article, I talked about the success of our goal of observing recently discovered (within the previous few weeks) asteroids within a few days of Full Moon. Most observatories usually avoid observing during this period because the bright Moon makes it impossible to see the fainter asteroids. It is like trying to observe in twilight. However, in some cases, if an asteroid is not observed during this period, it will be too faint as it moves away from us, or its position on the sky too uncertain for it to be observed in a week or two after this time, i.e., it may be lost.
Our Goal: Reduce Orbital Uncertainty, Making Future Detections More Likely, and Reducing the Probability of a Future Impact:
I suspect that many of you have seen a recent example of the importance of reducing the uncertainty of the orbiting of an asteroid— 2024 YR4. Soon after its discovery, there was a 3.1% chance that this asteroid would hit the Earth in 2032. As more and more observations over a longer period of time were made, the uncertainty in its orbit decreased to the point where there is no longer a threat to the Earth. However, there is still a greater than 3% chance that it will hit the Moon. If you had followed the updates reported in the news, you would have seen that, initially, the uncertainty in the time of closest approach to the Earth went from over 18 hours to about 1.5 hours. During that time, the actual orbit of the asteroid changed very little. Almost all of the impact uncertainty was related to where in its orbit the asteroid would be.
Have you ever seen an old movie car chase? Will the good guy (or the bad guy) outrun the car that is chasing them and make it over the railroad tracks before the train cuts them off or runs into them? Think of it this way. The big asteroid is the train, and a small Earth is your car. You know exactly where you are and when you will be crossing the railroad tracks. The train is scheduled to pass by the crossing at a certain time. In theory, you will cross the tracks after the train has passed by. However, if the train is behind schedule, you may be at the crossing just as the train is passing by! You have no way of knowing in advance where the train will really be.
The goal of observing NEOs is to reduce the uncertainty in the orbital parameters of the asteroid. With more observations over a period of a few weeks, you decrease the uncertainty in where the asteroid will be in future close approaches to the Earth, making it less likely that the asteroid will be lost. Just as important, more observations will decrease the chance that it will hit the Earth in the future (we hope).
Image 6: The uncertainty in the relative positions of the Earth and asteroid 2024 YR4, predicted at its closest approach on December 22, 2032, based on observations made through early January of 2025.
Image 7: The uncertainty in the relative positions of the Earth, Moon, and asteroid 2024 YR4, predicted at its closest approach on December 22, 2032, based on observations made through April of 2025. Note that the path of the asteroid (its orbit) has not changed, just the uncertainty in where it is in its orbit when it passes by the Earth.
Selecting, Detecting, Measuring, and Reporting Asteroid Observations
I will not get into the details of calibration, focusing, collimation, etc., as they are beyond the scope of this article. At the beginning of the night, Mark prints out a list of about 50 potential asteroids of interest. This is called the Plan Summary and was developed by Robert. For each asteroid, there is valuable information: the asteroid name, its priority (PHO, for example), how long since it was last observed, its magnitude, how fast it is moving, etc. Mark, at the telescope control computer, named “Don,” and I, the camera operator and keeper of the observing log, determine what our next object will be—is it observable at this time of night? Is it bright enough? Does its uncertainty put it within our field of view? Is it an object of interest? Mark then runs a program to determine the position of the asteroid, how fast it is moving so we can track it, and how long we have to integrate in order for there to be sufficient signal for Robert to find it and measure its position and magnitude (how bright it is).
Mark then slews the telescope to the appropriate field and sets the telescope to track at the rate of the asteroid’s predicted motion. I keep a detailed log of our observations—weather conditions that may affect our observing, the filter we are using for our observations, the object we are observing, the file name where the image is stored, integration time, and time of the observation. Some of this information is stored with the image, but not all.
We use the European Space Agency-supported NEODyS-2 (Near Earth Objects ˗ Dynamic Site) for orbital elements and on-sky uncertainties. Below is an example of what NEODyS-2 provides. The green line gives the direction of motion and speed, and the red error ellipse is the positional uncertainty for the requested time of observation. The field of view (blue square) is that of the VATT, 12.5 arcminutes on a side (the Moon is about 30 arcminutes across). The size and shape of the ellipse are determined by the uncertainty in the orbital elements of the asteroid and where it is relative to the Earth, both of which are moving objects. In the case of 2025 OZ2, the uncertainty is primarily due to one orbital parameter, where the asteroid is in its orbit.
Image 8: NEODyS-2 output for asteroid 2025 OZ2
We then make our observations. We need at least three positive detections of the asteroid which should be within the uncertainty ellipse predicted from prior observations. Once an image has been taken, Robert starts the analysis. If there is not enough signal, we will adjust the integration times. The asteroid is moving relative to the background stars. Sometimes the image of the asteroid blends with a nearby star. Robert cannot use the image to accurately measure the position of the asteroid. When this happens, Robert will ask us for an additional observation. Below is an example of three detections of the asteroid 2025 JB1, an NEO that we observed on June 13, 2025. Since I try to keep a complete observing log (as I emphasize with teachers and their students), I can say that we took three images that were 80 seconds each and separated by 2 minutes so that there was a reasonable spacing between the images.
Image 9: I have overlayed three images of the field including asteroid 2025 JB1. Between images, the asteroid moved relative to the background stars. The telescope tracked at the predicted rate of the asteroid, so the individual asteroid images are points, while the star images are elongated during the 80-second exposures.
Once Robert has determined the position and magnitude of each observation, he submits the result to the Minor Planet Center (MPC). “The Minor Planet Center is the single worldwide location for receipt and distribution of positional measurements of minor planets, comets and outer irregular natural satellites of the major planets. The MPC is responsible for the identification, designation and orbit computation for all of these objects.” Each morning, the MPC posts what is called the Minor Planet Electronic Circular Daily Orbit Update. These circulars contain all of the accepted asteroid observations (such as our observations) as well as updated orbital elements for these asteroids. The updated asteroid information is also available through the Jet Propulsion Laboratory (all asteroids) and through NEODyS (only NEOs). We use all three sites for planning and for analysis of our results.
2025 Update, Our Most Successful Year:
As I mentioned in my previous article, from 2015 through June of this year we have observed over 120 NEOs. Telescope scheduling is done by semester. 2025A ran from February 1 to early July and 2025B is from mid-September to the end of January. The telescopes are usually shut down during the summer monsoon season. This is a time also used for telescope maintenance. We had four scheduled observing runs in 2025A. Our first run in 2025A was an engineering run in which Robert tested out the software to help automate telescope focusing and collimation. We then had three regular observing runs, two right after Full Moon and another farther from Full Moon that allowed us to observe fainter asteroids (primarily asteroids that had not been observed for a year or more). This was a new program for us on the VATT. In 2025B, we are scheduled for three more observing runs starting in late September. This has been, by far, the most successful year for us, even though we are only halfway through the year. In 2022, our previous most successful year, we submitted 34 asteroids to the MPC. So far this year, we have observed 37 asteroids! Several of these asteroids were observed more than once during a run to improve their orbits. Five of these asteroids had not been observed in more than a year.
Two asteroids are worth highlighting.
- 2025 JB1: There were many observations of this asteroid, discovered in early May, but the last observations of it were on May 30 and there was still a fairly long-term uncertainty in its orbit. There had been two weeks without any observations when we made our observations a few days after Full Moon. It would be five days before more observations were made by the Catalina Sky Survey (CSS). Our observations reduced the orbital uncertainty by 75%. With the addition of the two nights’ observations by CSS, the uncertainty was small enough to allow the MPC to connect 2025 JB1 with another asteroid that had not been observed in 20 years, 2005 JF108.
- 2024 JB15: This was a recovery observation. After a year without any additional observations, the asteroid’s position in the sky (its error ellipse), was fairly large (about 30 arcseconds, 1/60 the diameter of the Moon). Therefore, the IAU requires that detections need to be made on two separate nights to ensure that its motion in the sky is consistent with the target asteroid and not some other, previously unidentified, asteroid. We made observations (three detections each night) on two nights before the IAU released the observations and the updated orbital elements. Our observations reduced its error ellipse around the time of this close approach by at least a factor of 10. Because of this reduction, connections were made to previously unreported detections more than a week earlier as well as previously unreported detections made in 2010. We thought that we were extending the observational arc for the asteroid’s orbit from 54 days (the 2024 observations) to 392 days (the inclusion of our new observations). Instead, the orbit was extended to 5,481 days! The long baseline of observations reduced the error ellipse at the next close approach of 2024 JB15 in April 2038 from over 4 arcminutes to less than 4 arcseconds!
Image 9a: One of the three detections of asteroid 2024 JB15. The blue line is the path of the asteroid (the length is the asteroid’s motion in 1 hour). Inside the error ellipse, you can see the observed position of the asteroid.
Figure 9b: The same detection, but enlarged so that you can see the asteroid more clearly.
I am writing this in mid-September and our first of three observing runs is at the end of the month. The forecast is for clear weather. We have had three productive observing runs this year and I look forward to three more through the end of the 2025B observing period. I hope to report to you about these runs early next year.
Mark Trueblood is the Director of the Winer Observatory in Sonoita, AZ, and is an instrument specialist. He oversaw the design and construction of instruments for the 8-m Gemini telescopes, and later for NOAO’s 4-m telescopes. He has co-authored two books about robotic telescopes, Microcomputer Control of Telescopes and Telescope Control. He headed the committee that made the recommendation for the new VATT CCD camera, critical for making remote observing on the VATT possible. Asteroid 15522 Trueblood is named in honor of his service to the astronomical community.
Robert Crawford is a retired energy and environmental consultant. As a high school student he computed his first asteroid orbit using an electro-mechanical tabulator (see below). He handles the detection and measurement of the asteroids we observe, having developed the software we use in observing and reporting our observations. He is also designing software to automate focusing and collimation of the VATT. Asteroid 57359 Robcrawford is named in his honor for his work in asteroid astrometry and photometry.
