Physical Considerations for an Intercept Mission to a 1I/'Oumuamua-like Interstellar Object

Brief

Ten authors from Harvard, CfA, STScI, and Wellesley model LSST detection yields and intercept feasibility for 'Oumuamua-class interstellar objects, adopting a number density of n~0.1 AU⁻³ and a velocity dispersion of σ~40 km/s. They find a mean expected LSST yield of ~15 detections over 10 years (95% Poisson CI: 0.38–84) and show that a 50 cm aperture spacecraft approaching to ~10³ km at 50 km/s produces ~1 m linear resolution and a ~10⁴-pixel image of a 100 m object in a ~20 s encounter window. Mission success probability is a steep function of ΔvUL: ~85% at 30 km/s, ~50% at 15 km/s, ~33% at 10 km/s. Optimal target size is between 1/3 and 1× 'Oumuamua's diameter, balancing detection rate against achievable resolution.

Metadata

Category

Search

Venue

Journal of Astronomical Instrumentation

Type

Peer-reviewed

Year

2023

Authors

Amir Siraj, Abraham Loeb, Amaya Moro-Martin, Mark Elowitz, Abigail White, Wesley A. Watters, Gary J. Melnick, Richard Cloete, Jonathan Grindlay, Frank Laukien

DOI

10.1142/S2251171723400019

arXiv

2211.02120

Access

Open access

Length

1.8 M

Programs

Galileo Project, ESA Comet Interceptor, NASA Bridge, Vera C. Rubin Observatory LSST

Instruments

Vera C. Rubin Telescope / LSST, Pan-STARRS, Spitzer Space Telescope

Data sources

Pan-STARRS survey, Hoover et al. 2022 dynamical simulations, CNEOS 2014-01-08 fireball catalog

Tags

interstellar objects, mission design, SETI, technosignature, survey science, astrobiology

Key points

• LSST expected mean yield is ~15 'Oumuamua-like ISOs over 10 years; 95% Poisson CI is 0.38–84, with a ~6% probability of zero detections and ~20% probability of only one detection in the first three years.p.5
• A 50 cm aperture at closest approach b~10³ km and encounter speed 50 km/s gives ~1 m linear resolution, producing a ~10⁴-pixel image of a 100 m object with a ~20 s data collection window.p.4
• Mission success probability scales steeply with delta-v budget: ~85% at ΔvUL ~30 km/s, reduced to a coin-flip at 15 km/s, and ~33% at 10 km/s, assuming immediate payload launch on detection.p.6
• ESA Comet Interceptor's ΔvUL ~15 km/s budget implies only a ~0.02% probability of intercepting an 'Oumuamua-like ISO within 10 years; relaxing size to 1/3 'Oumuamua raises this to ~0.04–15%.p.6
• LSST ISO detection rate follows a d³ volume scaling up to ~1 AU from Earth; objects smaller than 1/3 'Oumuamua's size are undetectable because orbital crossing time falls below the ~10-day threshold needed for three detections to constrain an orbit.p.5
• The size-distribution index q~3.5, inferred from CNEOS 2014-01-08, implies ~50 ISOs at H~25 detectable by LSST (95% CI: 1.3–280).p.5
• Optimal target size for maximizing mission success is between 1/3 and ~1× 'Oumuamua's diameter, trading off detection rate (which rises for smaller objects) against linear imaging resolution.p.6
• Reflectance spectroscopy at 0.4–2.5 μm during a close flyby can discriminate silicate, carbonaceous, and icy mineral classes, potentially distinguishing natural planetesimals from artificial constructs.p.7

Verbatim

• “we find that 0 . 38 − 84 'Oumuamua-like interstellar objects are expected to be detected in the next 10 years, with 95% confidence.”

  p.1

• “A close approach of b ∼ 10 3 km with a D ∼ 50 cm telescope would allow for linear resolution of ∼ 1 m, which would produce a ∼ 10 4 pixel image of an object with a size of ∼ 100 m.”

  p.4

• “The planned budget for ESA's Comet Interceptor mission (Jones & ESA Comet Interceptor Team 2019; Pau S´ anchez et al. 2021), ∆ v U L ∼ 15 km s − 1 , gives a ∼ 0 . 02% and & 0 . 04% (but . 15%) likelihood of finding a suitable target within 10 years, for 'Oumuamua-like objects and objects (1 / 3) the size of 'Oumuamua, re- spectively.”

  p.6

Most interesting

• 'Oumuamua (55–130 m) was detectable by Pan-STARRS only because it happened to pass unusually close to Earth on its outbound trajectory, at any typical detection distance it would have been invisible.
• 2020 SO mimicked all of 'Oumuamua's anomalous signatures, non-gravitational acceleration, no cometary outgassing, and was later confirmed to be NASA's own lost 1966 Surveyor 2 rocket booster, its thin metal walls producing a radiation-pressure effect.
• 2I/Borisov's CO-to-H₂O abundance ratio exceeded three times that of any comet in the inner solar system, implying formation in the outermost region of its parent planetary system.
• There is a 6% probability that LSST detects zero 'Oumuamua-like objects across its entire 10-year mission despite a mean expected yield of 15, the uncertainty range spans more than two orders of magnitude.
• A spacecraft encounter window at ~10³ km closest approach and 50 km/s lasts only ~20 seconds, yet this is sufficient for sub-meter resolved imaging if the aperture is 50 cm or larger.
• The Spitzer telescope ruled out the level of CO outgassing that would have been needed to explain 'Oumuamua's non-gravitational acceleration via the rocket effect, the required mass fraction (~10%) would have been detectable.