Two large asteroids pass the Earth safely just 42 hours apart

2024 MK – less than two weeks between discovery and flyby

Asteroid 2024 MK is between 120 and 260 m in size and was discovered on June 16, 2024. The asteroid will fly past Earth on June 29 at the peak of this year’s Asteroid Day activities.

2024 MK is large for a near-Earth object (NEO) and will pass by the Earth’s surface at a distance of 290,000 km—about 75% of the distance between the Earth and the Moon.

There is no risk of 2024 MK impacting Earth, but an asteroid of this size would cause significant damage if it did, so its discovery just a week before it passes our planet underscores the ongoing need to improve our ability to detect and monitor potentially hazardous near-Earth objects (NEOs).

Because of its size and proximity, 2024 MK can be observed on 29 June by amateur astronomers in some parts of the world using a small telescope or good binoculars under clear, dark skies. Plan your observations using ESA’s NEO toolkit.

(415029) 2011 UL21 – larger than 99% of near-Earth asteroids

Asteroid (415029) 2011 UL21 is the largest of this week’s visitors. With a diameter of 2310 m, this asteroid is larger than 99% of all known near-Earth objects (NEOs). However, it will not come nearly as close to Earth. At its closest point on June 27, it will still be more than 17 times as far away as the Moon.

This asteroid’s orbit around the Sun is steeply inclined, which is unusual for such a large object. Most large objects in the Solar System, including planets and asteroids, orbit the Sun in or near the equatorial plane.

This could be the result of gravitational interaction with a large planet like Jupiter. Jupiter can deflect previously harmless asteroids inward toward Earth, so it is important to understand this process.

(415029) 2011 UL21 is in an “11:34 resonance” with the Earth. It completes 11 revolutions around the Sun in almost exactly the same time that the Earth completes 34 revolutions (i.e. 34 years).

The result is a pleasant, repeating pattern if you visualize the asteroid’s position relative to Earth over a period of 34 years while keeping Earth fixed in its position.

Asteroid Day 2024

The impact craters that mar the Earth’s surface are evidence of how much asteroids have influenced the history and evolution of our planet.

Recognized by the United Nations, Asteroid Day commemorates the largest asteroid impact in recorded history – the 1908 air detonation over Tunguska in largely deserted Siberia, which brought down around 80 million trees.

For Europe, it was fortunate that the incident occurred only a short distance away from the Earth’s rotation and did not affect the more densely populated regions of the continent.

Thanks to the cooperation and support of its Member States, ESA is in a unique position to coordinate the data, information and expertise needed to understand and respond to asteroid hazards in Europe and to contribute to humanity’s broader efforts to protect the planet.

Over the past two decades, ESA has discovered and analysed potentially hazardous NEOs. An estimated 5 million NEOs are larger than 20 metres – the limit at which an impact could cause damage to the ground.

ESA intensifies asteroid activities

ESA’s Planetary Defence Office is carrying out a number of projects aimed at improving our ability to detect, track and contain potentially dangerous asteroids.

ESA’s Hera mission, launching later this year, is part of the world’s first test of asteroid defence. Hera will conduct a detailed study of the asteroid Dimorphos after the impact of NASA’s DART mission in September 2022, helping to transform the experiment into a well-understood and repeatable planetary defence technique. Members of the Hera team will take part in Asteroid Day celebrations later this week.

On Earth, ESA is currently developing a network of insect-style Flyeye telescopes, which will use their uniquely wide field of view to automatically scan the entire sky every night for new, potentially dangerous asteroids.

Our future satellite, NEOMIR, will be stationed between the Earth and the Sun. It will use infrared light to detect asteroids approaching our planet from regions of the sky that are not visible from the ground because they are obscured by the glare of our star.

Meanwhile, the Planetary Defence Office is still closely monitoring the skies today. ESA’s fireball camera in Cáceres, Spain, captured a stunning meteor on the night of 18-19 May 2024, believed to be a small piece of a comet that flew over Spain and Portugal at around 162,000 km/h before burning up over the Atlantic.

Just a few weeks later, on June 6, 2024, the Catalina Sky Survey in Arizona, USA, discovered a small asteroid measuring 2–4 m, which triggered an alert from ESA’s impact monitoring system (Meerkat). This alert did not refer to an impact, but to a very close incident. A few hours later, the object flew over the Catalina Sky Survey telescope, which detected it at a distance of just 1750 km, making it the second-closest flyby of a known non-impacting asteroid ever.