# Implications of evaporative cooling by H$_2$ for 1I/`Oumuamua

**Authors:** Thiem Hoang, Abraham Loeb  
**arXiv:** [2303.13861](https://arxiv.org/abs/2303.13861)  
**Date:** 2023-03-24  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2303.13861v1/

## Key points

- In 2017, the first interstellar object observed in our solar system, 1I/`Oumuamua, exhibited several peculiar properties.
- A recent study by Bergner and Seligman (2023) proposed that evaporation of trapped H$_2$ created by cosmic rays (CRs) can explain the non-gravitational acceleration.
- However, a new study by Thiem Hoang and Abraham Loeb has shown that Bergner and Seligman's calculation of surface temperature ignored the crucial cooling effect of evaporating H$_2$.
- By taking into account the cooling by H$_2$ evaporation, they found that the surface temperature of H$_2$-water ice is lower than the temperature obtained by Bergner and Seligman (2023) by a factor of 9.
- This means that the thermal speed of outgassing H$_2$ is decreased by a factor of 3. As a result, all H$_2$ from water ice would need to be dissociated by CRs in the interstellar medium, making Bergner and Seligman's model untenable as an explanation for the properties of 1I/`Oumuamua.
- Hoang and Loeb also found that the lower surface temperature influences the thermal annealing of water ice which is a key process appealed to by Bergner and Seligman (2023).
- The lower surface temperature means that less energy is available for thermal annealing to occur. Therefore their results suggest that alternative explanations are needed for the peculiar properties observed in 1I/`Oumuamua.
- This study highlights how important it is to consider all relevant physical processes when developing models to explain astronomical observations.
- It also demonstrates how scientific knowledge can evolve through ongoing research and refinement.
- First interstellar object observed in our solar system, 1I/`Oumuamua, exhibited peculiar properties
- Bergner and Seligman (2023) proposed evaporation of trapped H$_2$ created by cosmic rays can explain non-gravitational acceleration
- Hoang and Loeb found Bergner and Seligman's calculation of surface temperature ignored crucial cooling effect of evaporating H$_2$
- Surface temperature of H$_2$-water ice is lower than temperature obtained by Bergner and Seligman (2023) by a factor of 9
- Thermal

## Summary

In 2017, the first interstellar object observed in our solar system, 1I/`Oumuamua, exhibited several peculiar properties, including extreme elongation and non-gravitational acceleration. A recent study by Bergner and Seligman (2023) proposed that evaporation of trapped H$_2$ created by cosmic rays (CRs) can explain the non-gravitational acceleration. However, a new study by Thiem Hoang and Abraham Loeb has shown that Bergner and Seligman's calculation of surface temperature ignored the crucial cooling effect of evaporating H$_2$. By taking into account the cooling by H$_2$ evaporation, they found that the surface temperature of H$_2$-water ice is lower than the temperature obtained by Bergner and Seligman (2023) by a factor of 9. This means that the thermal speed of outgassing H$_2$ is decreased by a factor of 3. As a result, all H$_2$ from water ice would need to be dissociated by CRs in the interstellar medium, making Bergner and Seligman's model untenable as an explanation for the properties of 1I/`Oumuamua. Hoang and Loeb also found that the lower surface temperature influences the thermal annealing of water ice which is a key process appealed to by Bergner and Seligman (2023). The lower surface temperature means that less energy is available for thermal annealing to occur. Therefore their results suggest that alternative explanations are needed for the peculiar properties observed in 1I/`Oumuamua. This study highlights how important it is to consider all relevant physical processes when developing models to explain astronomical observations. It also demonstrates how scientific knowledge can evolve through ongoing research and refinement.