Killer Asteroids – Are they??

Protecting Humanity!

A hosted article by Ilavenil T

 

“Extinction is the rule. Survival is the exception” - Carl Sagan

 

Biennial exercises by NASA simulate asteroid impacts to prepare international response strategies. Scenarios like these use real data to test emergency preparedness and explore deflection techniques like the DART mission.

 

Ilavenil T

This is Ilavenil’s second article as a guest blogger under my banner. The first one appeared in February this year and can be accessed here.  

On the theme of potentially dangerous near-earth objects, the present article is both complementary and supplementary to my own in September 2023 (see here), which had been inspired by her involvement in asteroid hunting as a Regional Training Volunteer in the International Astronomical Search Collaboration (IASC).  

[This article appears as an interlude to the present series of articles on Pioneers of Quantum Theoretical Physics commemorating the International Year of Quantum Science and Technology, IYQ25.]

The portents

We all saw headlines and videos like these in January and February 2025:

Astronomers spot asteroid that may be heading for the earth. The Hindu (Feb 5, 2025)

UN monitors asteroid with a tiny chance of hitting Earth.  BBC (Feb 3, 2025)

Revised Calculations Just Increased Asteroid 2024 YR4's Chances of Hitting Earth (Odds: 1-in-43)  (TerritorySpace Youtube Channel, February 8, 2025)

Not only was the media talking about an impending impact on Earth, a map was also published showing the probable areas where it could happen, including a line right across India (see map below). This was just scare mongering.

After a month or so, the threat was deescalated. However, these reassuring articles did not go viral as the initial ones did.

Here are some valid questions about these scary portents:

·      Why do the media report possible asteroid impacts so often?

·      An asteroid will never hit the Earth, right?

·      What is being done about it?

In this article I’ll attempt to answer these questions.

Why do they report possible asteroid impacts so often?

The announcements keep coming because there are literally hundreds of NEOs (Near-Earth Objects) that cross the Earth’s orbit every year. NEOs are asteroids and comets that orbit the Sun with a perihelion distance* less than 1.3 au^@. According to the Centre for Near Earth Object Studies (CNEOS), there are 17 objects that will come within a distance of 5 lunar distances within the next year (between April 26, 2025 and April 26, 2026). One of them will come even closer than the Moon.

[*Perihelion distance: The closest distance between an object and the Sun.

^@ au: Astronomical Unit – the average distance between the Earth and the Sun - 149,597,870 km]

Here are the orbits of the five NEOs that will come the closest within the next year, generated through the CNEOS orbit viewer.

 

The following table* shows close approaches to the Earth by near-Earth objects (NEOs)

Object	Close-Approach (CA) Date	CA Distance Nominal (LD)	CA Distance Minimum (LD)
2025 HW1	2025-Apr-28 17:41 ±    00:06	3.160	3.137
2025 FA22	2025-Sep-18 07:04 ±    03:33	2.162	2.022
2025 DQ	2026-Feb-21 17:53 ±    00:08	3.018	2.957
2025 BL	2026-Jan-17 07:14 ±    01:31	4.663	4.171
2024 TB7	2026-Apr-07 14:21 ±    07:17	4.848	2.330
2023 PX	2025-Aug-22 11:21 ± 1_10:07	2.416	2.413
2023 DZ2	2026-Apr-04 02:01 ±    00:02	2.633	2.633
2023 CM2	2026-Feb-21 12:56 ± 8_10:52	4.164	1.999
2022 SS2	2025-Sep-13 15:22 ± 3_03:06	2.369	1.847
2022 OB5	2026-Jan-14 07:21 ± < 00:01	1.679	1.679
2022 OC3	2026-Jan-31 23:41 ±    01:49	1.301	1.288
2021 PJ1	2025-Aug-15 04:38 ±    01:52	4.357	4.074
2015 XX168	2025-Dec-18 20:34 ±    07:53	4.693	1.670
2015 VO142	2026-Mar-17 05:12 ±    07:10	2.715	2.396
2013 GM3	2026-Apr-14 16:15 ±    07:56	0.678	0.020
2010 RA91	2026-Mar-22 01:13 ±    00:01	4.671	4.669
2007 EG	2026-Mar-15 02:24 ± < 00:01	4.457	4.457

CA Distance Nominal: The most likely closest-approach distance (centre of the Earth to centre of the NEO)

CA Distance Minimum: The minimum possible close-approach distance (centre of the Earth to centre of the NEO)

LD: Lunar Distance - the mean semi-major axis length of the orbit of the Moon around the Earth - 384400 km. 384400 km.

*From: https://cneos.jpl.nasa.gov/ca/

Even though the numbers are large, the distances are also large. For example, the mean minimum closest approach distance of the objects in the table is 9,89,549 km. That is almost four times the distance between the Earth and the Moon. As for the object that will come closer than the Moon, it is only between 15 - 33m in size. It will burn up even if it touches the Earth’s atmosphere.

In addition to this, bolides and fireballs (unusually bright meteors) are tracked regularly. These also number in the hundreds, as seen in the map below.

From: jpl.nasa.gov

Though the map may look frightening, it is important to remember that these are fragments of comets and asteroids which burnt up in the atmosphere without actually impacting the Earth. These numbers show why there are so many announcements of asteroids coming close to the Earth.

An asteroid will never hit the Earth, right?

The answer to this question might be disheartening. Asteroid impacts are regular occurrences, and have occurred many times on the Earth in its past history.

Some of the largest impact structures on the Earth are*:

#	Crater Name	Age (Years)	Location	Diameter (km)
1	Vredefort Crater	2,023,000,000	South Africa	(170 – 300)
2	Sudbury Basin	1,849,000,000	Canada	130
3	Acraman Crater	~590,000,000	Australia	Up to 90
4	Woodleigh Crater	~364,000,000	Australia	~120
5	Manicouagan Crater	214,000,000	Canada	100
6	Morokweng Crater	146,000,000	South Africa	75 - 150
7	Kara Crater	70,300,000	Russia	~120 before erosion
8	Chicxulub Crater	66,000,000	Mexico	200
9	Popigai Crater	35,700,000	Russia	90
10	Chesapeake Bay Crater	35,500,000	United States	85

Information compiled from Wikipedia

*There are other structures similar to impact craters, some even larger, which are still under investigation about the probable cause.

Looking at the table, there seems to be a trend where the craters become smaller as we move from the past to the present. That is not true – the actual reason is that the larger the crater, the better it withstands the geologic processes of the Earth, such as erosion and the rock cycle, where rocks are transformed from one type to another.

The Vredefort crater in South Africa was the result of the Earth being hit by an impactor that was 20-25 km in diameter. It did not cause a mass extinction since the Earth was inhabited only by unicellular organisms at the time. However, the impactor that caused the extinction of almost 75% of species was between 10-15 km in diameter.

This is a satellite image of the Vredefort impact structure, with the Vaai river running across it.

A closer look on Google maps shows a farming town, highways and a nature park, all inside the crater!

Here are the locations of some of the largest impacts on earth:

The interactive form of this map, with details on all the craters, is available at https://upload.wikimedia.org/wikipedia/commons/c/cc/Earth_Impact_Database_world_map.svg

It is highly probable that we will be hit with a large impactor in the future.

What is being done about this?

Protecting humanity from a species-ending asteroid (or comet) strike is the main objective of Planetary Defence. The term “Planetary defence” includes the detection, tracking, and avoidance of potential asteroid impacts on Earth. It is led by NASA's Planetary Defense Coordination Office (PDCO).

Detection and Tracking

The detection and tracking of Near-Earth Objects, including asteroids and comets, is important not only for planetary defence but also to accurately map the solar system and improve our understanding of gravitational perturbations. (Gravitational perturbations are small changes in a celestial body’s orbit when another body passes near it, and they happen because of the gravitational force between the objects).

This is currently being done using a combination of ground-based telescopes, space telescopes and citizen science initiatives. All discoveries are logged in the catalogues of the Minor Planet Centre (MPC.)

NASA's NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) mission repurposed the Wide-field Infrared Survey Explorer (A NASA infrared space telescope) to detect and characterize asteroids and comets using infrared observations. It was decommissioned in August 2024.

The Catalina Sky Survey is conducted at the Steward Observatory's Catalina Station, located near Tucson, Arizona, in the United States. The Catalina Sky Survey (CSS) uses three telescopes, all located in the Catalina mountains - a 1.5 meter telescope and a 1m telescope on Mount Lemmon and a 68 cm telescope on Mount Bigelow. The telescopes search for NEOs, and operate on every clear night except a few around the full moon. As of 2020, the Catalina Sky Survey is responsible for almost 47% of new Near-Earth Object Discoveries.

The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS)

The Pan-STARRS system consists of two 1.8m telescopes located at Haleakala in Hawaii. They stand out in having very large fields of view and are equipped with digital cameras with short exposure. This adds up to a lot of observation and a lot of data to be analysed, which is why the system also includes a computing facility. In addition to surveying the sky for moving or variable objects, the Pan-STARRS system also produces accurate astrometry and photometry of existing objects.

A data release by Pan-STARRS in January 2019 was the largest volume of astronomical data ever released, at 1.6 petabytes.

Role of Citizen Scientists and the IASC in Spotting Asteroids

Citizen scientists play a vital role in asteroid detection through initiatives like the International Astronomical Search Collaboration (IASC). This program provides high-quality astronomical data to volunteers worldwide, enabling them to participate in asteroid discovery campaigns.

The citizen scientists, mainly school students and some interested adults, use a customized version of Astrometrica  - a software meant to precisely measure the positions and movements of celestial bodies - to analyse images and identify moving objects that may be asteroids. Their contributions have led to the discovery of thousands of asteroids, including near-Earth objects.

IASC has facilitated the discovery of approximately 12,000 main-belt asteroids and several near-Earth objects over the past 15 years, involving over 50,000 citizen scientists from 96 countries.

I have worked with hundreds of students and eager adults as a Regional Training Volunteer in IASC. Here is a map of the provisional discoveries made by the people I have guided, as on October 16, 2024.

Image compiled using the Small body database

For more information on my work in this field and the procedure by which students detect asteroids, please check this: Asteroid Hunt

Databases

The discoveries are collated in the following databases:

The Minor Planet Center Orbit Database (MPCORB) is one of the most comprehensive catalogues. Managed by the Minor Planet Center, it includes orbital elements and physical properties for hundreds of thousands of known asteroids and other small bodies. It is updated daily and is considered the authoritative source for asteroid data globally.

NASA’s Jet Propulsion Laboratory (JPL) maintains the Small-Body Database, which provides highly detailed information on the orbital characteristics, ephemerides, and close-approach parameters of small solar system bodies. It also has an orbit viewer and links to different Application Programming Interfaces (APIs) for those who want to work with the data.

NASA’s CNEOS Sentry Database focuses on risk monitoring. It tracks potentially hazardous asteroids (PHAs) and calculates their probabilities of impacting Earth over the next 100 years.

Tracking asteroids

Once detected, an approximate orbit of the asteroid can be calculated, using the diameter or the absolute magnitude. However, this can change over months or years, as the mass of the asteroid will depend on the composition, not the diameter.

In addition to the mass, passing by celestial objects such as a planet, satellite or other asteroid will change the orbit. The Yarkovsky effect – a force that acts on a rotating body because of the non-uniform emission of thermal photons, is pronounced in asteroids because of their small sizes, and can also play a part in changing the orbit.

Hence, continuous and precise tracking is a major facet of planetary defence.

In the future:

The upcoming NEO Surveyor mission, scheduled for launch in 2027, is the first space telescope to be launched to detect potentially hazardous asteroids by using infrared space-based observations.

Asteroid Avoidance

DART (Double-Asteroid Redirection Test)

On 26 September 2022, the DART spacecraft collided with Dimorphos, a satellite of the asteroid Didymos.

It successfully shortened the orbit of Dimorphis by 32 minutes, showing that it was possible to change the orbit of a celestial body. Dimorphos has a diameter of 177m, and the successful change in orbit showed that it is possible for us to deflect an asteroid that might be on a collision course with Earth.

The change in orbit was due to the transfer of momentum, mainly by the recoil of the debris that was left by the impact more than the impact itself. DART took years to plan, starting from the proposal to the launch. In case of an imminent impact, we will still need months to build and launch the interceptor spacecraft. So, detection and mitigation go hand in hand.

Some more ways to deflect an asteroid

Gravity Tractor

A spacecraft hovers near the asteroid, using its gravitational pull to gradually pull the asteroid off course. It's a slow method but highly controlled and doesn't require contact with the asteroid's surface.

Nuclear Detonation

A nuclear device is detonated near or on the asteroid. A surface explosion could vaporize part of the asteroid, creating thrust through ejecta. A subsurface explosion would fragment it. This method is seen as a last resort due to political, legal, and risk-related concerns.

Mass Drivers or Railguns

Mechanical devices mounted on the asteroid eject mass from its surface, producing thrust over time. These are still theoretical and would require anchoring to the asteroid.

Albedo Modification

The Albedo is a measure of how reflective a celestial body is, which in turn will affect the Yarkovsky effect. By coating the asteroid with materials that increase or decrease the albedo, the Yarkovsky effect can be modified, changing the orbit.

Asteroid Approaches and the Public

The Torino scale was first adopted by the International Astronomical Union (IAU) in 1999. The Torino scale assigns a number to potential impacts by mapping the size (and the kinetic energy that will be released on impact) against the possibility of impact.

This is the explanation, according to CNEOS (reproduced verbatim)

No Hazard (White Zone)	0	The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage.
Normal (Green Zone)	1	A routine discovery in which a pass near the Earth is predicted that poses no unusual level of danger. Current calculations show the chance of collision is extremely unlikely with no cause for public attention or public concern. New telescopic observations very likely will lead to re-assignment to Level 0.
Meriting Attention by Astronomers (Yellow Zone)	2	A discovery, which may become routine with expanded searches, of an object making a somewhat close but not highly unusual pass near the Earth. While meriting attention by astronomers, there is no cause for public attention or public concern as an actual collision is very unlikely. New telescopic observations very likely will lead to re-assignment to Level 0.
	3	A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of localized destruction. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by public and by public officials is merited if the encounter is less than a decade away.
	4	A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of regional devastation. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by public and by public officials is merited if the encounter is less than a decade away.
Threatening (Orange Zone)	5	A close encounter posing a serious, but still uncertain threat of regional devastation. Critical attention by astronomers is needed to determine conclusively whether or not a collision will occur. If the encounter is less than a decade away, governmental contingency planning may be warranted.
	6	A close encounter by a large object posing a serious but still uncertain threat of a global catastrophe. Critical attention by astronomers is needed to determine conclusively whether or not a collision will occur. If the encounter is less than three decades away, governmental contingency planning may be warranted.
	7	A very close encounter by a large object, which if occurring over the next century, poses an unprecedented but still uncertain threat of a global catastrophe. For such a threat, international contingency planning is warranted, especially to determine urgently and conclusively whether or not a collision will occur.
Certain Collisions (Red Zone)	8	A collision is certain, capable of causing localized destruction for an impact over land or possibly a tsunami if close offshore. Such events occur on average between once per 50 years and once per several 1000 years.
	9	A collision is certain, capable of causing unprecedented regional devastation for a land impact or the threat of a major tsunami for an ocean impact. Such events occur on average between once per 10,000 years and once per 100,000 years.
	10	A collision is certain, capable of causing global climatic catastrophe that may threaten the future of civilization as we know it, whether impacting land or ocean. Such events occur on average once per 100,000 years, or less often.

The objective of defining this scale was to give the public a familiar standard to interpret any announcements of an asteroids’ close approach. Just as the Richter scale is familiar to the public now, and a level 3 earthquake does not trigger mass panic, it was expected that an announcement of a Level 1 collision probability would be met with interest and not fear.

However, the fearmongering does continue. It is important that most people are aware that they can check the truth behind these announcements themselves.

Here is a guide for people to interpret newspaper articles and videos, using the small body database.

A few successes of early asteroid detection

2024 YR – the most recent scare

​Asteroid 2024 YR4 was discovered on December 27, 2024, by the ATLAS survey in Río Hurtado, Chile. Initial observations indicated a potential Earth impact on December 22, 2032. On further observations, the probability of impact went up to 3.1% on February 18, 2025. This elevated its status to Level 3 on the Torino Scale, prompting global planetary defence initiatives. ​

However, subsequent observations led to a change in the calculated orbit, reducing the impact probability to 0.004%. The Torino scale rating was brought to 0.  However, there remains a 3.8% chance of 2024 YR4 impacting the Moon on December 22, 2032, which would offer a unique opportunity for scientific observation of crater formation. ​

Here are the orbits, as per present calculations, of the most probably positions of the Moon and asteroid 2024 YR4 on December 22, 2032.

Apophis – the biggest threat?

Asteroid 99942 Apophis was discovered in 2004 and initially raised significant concern due to its projected close approach to Earth on April 13, 2029. Early readings showed that Apophis might go through a “gravitational keyhole” – a narrow region of space near Earth. If it passed through, Earth’s gravity would have shifted its orbit enough to set it on a collision course with Earth on the next approach (2036). However, this possibility has now been ruled out.

But, the 2029 close orbit of Apophis is going to be at a distance of just 32,000 km from Earth’s surface. This will allow close observation of its orbital parameters.

What to look for in an article

Look for the number or name of the asteroid – this is mentioned in every video clip or webpage.

Go to the Small Body Database of NASA: https://ssd.jpl.nasa.gov/

This is a rich resource, but for a quick check, all that is needed is to see how close the asteroid will actually come to the surface of the Earth.

To do that, first enter the name or the number of the asteroid into the search bar and press ‘ENTER’.

A page will open up with all the details of that body, including an orbit viewer.

If the orbit viewer is not visible, click the [show] link.

Scroll down to the close approach data, which might also be hidden. The close approach data gives a list of the close approaches of the asteroid. For Apophis, the data is available from 1905 to 2117 (98 close approaches.)

To get the details of the closest approach, set the units to kilometres and click the up/down arrow icon in the “Minimum Distance” column.

This will arrange the close approaches in ascending order, with the closest approach listed first.

As you can see, the closest approach by Apophis is in 2029, at a distance of 38,008 km.

General observations

An asteroid impact is a definite threat to the human species, but unlike the other species who have witnessed an asteroid hitting the Earth, we have tools to observe and deflect an asteroid. It is important that the public is aware of the risks as well as the tools available.

Early detection is key in protecting ourselves. In addition to the agencies which are at work detecting and cataloguing, the public can also participate. I urge everyone to do their best – whether it is informing your friends and family about the exact nature of a news article, participating in an asteroid search or, if you are competent, analyse the data available on your own.

This is for humanity – we need all hands-on deck. 

References

1.     "Asteroid That May Be Heading for the Earth Spotted by Astronomers." The Hindu, 25 Apr. 2025, www.thehindu.com/sci-tech/science/astronomers-spot-asteroid-that-may-be-heading-for-the-earth/article69183574.ece.

2.      "Asteroid on Possible Collision Course with Earth, Scientists Warn." BBC News, 25 Apr. 2025, www.bbc.com/news/articles/cqx9dgpx98go.

3.     "Scientists Discover an Asteroid Headed for Earth." YouTube, uploaded by Territory, 25 Apr. 2025, www.youtube.com/watch?v=8hCbD2i72UM.

4.     "2024 YR4 Risk Corridor." Wikimedia Commons, uploaded 25 Apr. 2025, upload.wikimedia.org/wikipedia/commons/8/8a/2024_YR4_risk_corridor.png.

5.     NASA Center for Near Earth Object Studies. “Close Approaches.” NASA, https://cneos.jpl.nasa.gov/ca/. Accessed 23 Apr. 2025.​

6.     Jet Propulsion Laboratory. “New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population.” NASA, 22 Apr. 2014, https://www.jpl.nasa.gov/news/new-map-shows-frequency-of-small-asteroid-impacts-provides-clues-on-larger-asteroid-population/. Accessed 23 Apr. 2025.​

7.     "Meteors and Meteorites: Facts." NASA, 25 Apr. 2025, science.nasa.gov/solar-system/meteors-meteorites/facts/.

8.     "Vredefort Impact Structure." Wikipedia, Wikimedia Foundation, 25 Apr. 2025, en.wikipedia.org/wiki/Vredefort_impact_structure.

9.     NASA. “NEOWISE.” NASA Science, https://science.nasa.gov/mission/neowise/. Accessed 23 Apr. 2025.​

10.“Catalina Sky Survey.” Wikipedia, Wikimedia Foundation, https://en.wikipedia.org/wiki/Catalina_Sky_Survey. Accessed 23 Apr. 2025.​

11.“Pan-STARRS.” Wikipedia, Wikimedia Foundation, https://en.wikipedia.org/wiki/Pan-STARRS. Accessed 23 Apr. 2025.​

12.Minor Planet Center. “MPCORB Database.” International Astronomical Union, https://www.minorplanetcenter.net/iau/MPCORB.html. Accessed 23 Apr. 2025.​

13.NASA. “DART: Double Asteroid Redirection Test.” NASA Science, https://science.nasa.gov/mission/dart/. Accessed 23 Apr. 2025.​

14."Double Asteroid Redirection Test (DART)." Johns Hopkins Applied Physics Laboratory, 25 Apr. 2025, dart.jhuapl.edu/Mission/index.php.

15.Betts, Bruce. “Asteroid Deflection: Techniques to Save the Earth.” The Planetary Society, 1 Mar. 2023, https://www.planetary.org/articles/asteroid-deflection-techniques-to-save-the-earth. Accessed 23 Apr. 2025.​

16.Rumpf, Clemens, and Hugh G. Lewis. “Assessing the Impact Risk of Near-Earth Objects.” Acta Astronautica, vol. 211, 2024, pp. 1–10. ScienceDirect, https://www.sciencedirect.com/science/article/abs/pii/S0094576523005593. Accessed 23 Apr. 2025.​

17.Rumpf, Clemens, and Hugh G. Lewis. “Probabilistic Impact Risk Assessment for Near-Earth Objects.” Acta Astronautica, vol. 177, 2020, pp. 1–10. ScienceDirect, https://www.sciencedirect.com/science/article/abs/pii/S0094576520305634. Accessed 23 Apr. 2025.​

18.NASA. “Asteroid 2024 YR4.” NASA Science, https://science.nasa.gov/solar-system/asteroids/2024-yr4/. Accessed 23 Apr. 2025.​

19.NASA. “Apophis.” NASA Science, https://science.nasa.gov/solar-system/asteroids/apophis/. Accessed 23 Apr. 2025.​

20.Thomson, Elizabeth A. “Revised Asteroid Scale Aids Understanding of Impact Risk.” MIT News, 12 Apr. 2005, https://news.mit.edu/2005/torino. Accessed 23 Apr. 2025.