How many near-Earth objects are there? When will earth be hit again?

A real climate crisis would happen if a large enough asteroid hits earth! These events are very rare, but when was the last major impact?

"Near-Earth objects (NEOs) are asteroids that orbit close to Earth. Surveys have found numerous NEOs, but the list is known to be incomplete. ... combined survey data and orbit modeling to determine the completeness of NEO surveys and then estimate the true underlying population. They inferred that there are about 900 NEOs larger than 1 kilometer in diameter, of which 91% have been detected. Smaller NEOs, some of which have been produced by tidal disruption of larger asteroids that passed close to planets, have lower detection rates. The authors calculated the chance of impact on Earth by a city-destroying (or larger) asteroid to be 4.5% over the next thousand years."

From the highlights:

"Highlights

• Catalina Sky Survey observations (2013–2022) are used to update our NEO model.

• There are NEOs with absolute magnitude ¡17.75.

• The population of very small NEOs is boosted by tidal disruption of large NEOs.

• We estimate  impacts of ¡28 NEOs on the Earth per year.

• The impact probability of a ¡22 NEO on the Earth in this millennium is 4.5%."

From the abstract:

"Catalina Sky Survey (CSS) is a major survey of Near-Earth Objects (NEOs). In a recent work, we used CSS observations from 2005-2012 to develop a new population model of NEOs (NEOMOD). CSS's G96 telescope was upgraded in 2016 and detected over 10,000 unique NEOs since then. Here we characterize the NEO detection efficiency of G96 and use G96's NEO detections from 2013-2022 to update NEOMOD. This resolves previous model inconsistencies related to the population of large NEOs. We estimate there are 936+/-29 NEOs with absolute magnitude H<17.75 (diameter D>1 km for the reference albedo p_V=0.14). The slope of the NEO size distribution for H=25-28 is found to be relatively shallow (cumulative index 2.6) and the number of H<28 NEOs (D>9 m) is determined to be (1.20+/-0.04)x10^7. Small NEOs have a different orbital distribution and higher impact probabilities than large NEOs. We estimate 0.034+/-0.002 impacts of H<28 NEOs on the Earth per year, which is near the low end of the impact flux range inferred from atmospheric bolide observations. Relative to a model where all NEOs are delivered directly from the main belt, the population of small NEOs detected by G96 shows an excess of low-eccentricity orbits with a=1--1.6 au that appears to increase with H. We suggest that the population of very small NEOs is boosted by tidal disruption of large NEOs during close encounters to the terrestrial planets. When the effect of tidal disruption is (approximately) accounted for in the model, we estimate 0.06+/-0.01 impacts of H<28 NEOs on the Earth per year, which is more in line with the bolide data."

Science In Other Journals

NEOMOD 2: An updated model of Near-Earth Objects from a decade of Catalina Sky Survey observations (no public access)

NEOMOD 2: An Updated Model of Near-Earth Objects from a Decade of Catalina Sky Survey Observations (preprint version, open access)

Images from the CSS. See the purple circle!