A hypothetical asteroid impact scenario will be presented at the 2019 IAA Planetary Defense Conference (PDC), to be held in College Park, Maryland, USA, April 29 - May 3, 2019. Although this scenario is realistic in many ways, it is completely fictional and does NOT describe an actual potential asteroid impact. The scenario begins as follows:

An asteroid is discovered on March 26, 2019, at magnitude 21.1, and confirmed the following day. It is assigned the designation “2019 PDC” by the Minor Planet Center. (To reinforce the fact that this is not a real asteroid, we are using three letters in the designation, something that would never be done for an actual asteroid.)

Initial calculations indicate that the orbit of 2019 PDC approaches well within 0.05 au of the Earth’s orbit. (The unit “au” stands for “astronomical unit”, which is the mean distance of the Earth from the Sun, 149,597,870.7 km, or 92,955,807 miles.) Since the initial estimate of the asteroid’s absolute (intrinsic) magnitude H is 21.7, it qualifies as a Potentially Hazardous Asteroid (PHA).

The asteroid’s orbit is eccentric, extending from a distance of 0.89 au from the Sun at its closest point to 2.94 au at its farthest point in the middle of the main asteroid belt. Its orbital period is 971 days (2.66 years), and its orbital plane is inclined 18 degrees to the Earth’s orbital plane.

The day after 2019 PDC is discovered, JPL’s Sentry impact monitoring system, as well as ESA’s similar CLOMON system, both identify several future dates when this asteroid could potentially impact the Earth. Both systems agree that the most likely potential impact occurs on April 29, 2027 - over eight years away - but the probability of that impact is very low, about 1 chance in 50,000. With only two days of tracking this object, no more definitive statement can be made.

When first detected, the asteroid is about 0.38 au (57 million kilometers or 35 million miles) from Earth, approaching our planet at about 14 km/s (8.5 mi/s or 31,000 mph), and slowly getting brighter. 2019 PDC is observed extensively for a few weeks after discovery, and as the observational dataset grows, the impact probability for 2027 increases. Three weeks after discovery, when observations pause during full moon, the impact probability has risen to nearly 0.4 percent, or about 1 chance in 250. The asteroid continues to brighten somewhat as it approaches, but it reaches a peak brightness of only 20.3 at the end of April.

Very little is known about the asteroid’s physical properties. Based on the apparent visual magnitude, its absolute (intrinsic) magnitude is estimated to be about H = 21.7 +/- 0.4. Since its albedo (reflectivity) is unknown, however, the asteroid’s mean size could be anywhere from roughly 100 meters to over 300 meters.

2019 PDC approaches the Earth for well over a month after discovery, and it reaches its closest point of about 0.13 au on May 13. Unfortunately, the asteroid is too far away to be detected by radar, and it is not expected to pass close to the Earth again, until 2027.