# Detection of Extrasolar Planets by Gravitational Microlensing

**Authors:** David P. Bennett  
**arXiv:** [0902.1761](https://arxiv.org/abs/0902.1761)  
**Date:** 2009-02-10  
**Summary page:** https://www.summarizepaper.com/en/paper/0902.1761v1/

## Key points

- Gravitational microlensing is a powerful method for studying extrasolar planetary systems
- It allows for the detection of low-mass planets at separations of a few AU from their host stars
- Recent evidence suggests that "super-Earth" planets are the most common type of exoplanet detected so far
- Two super-Earth planets have been detected, indicating that roughly one third of stars in our galaxy may have similar planets within the separation range of 1.5-4 AU
- Microlensing occurs when a foreground object passes in front of a background star and causes a temporary magnification or brightening effect
- By monitoring these brightness variations, astronomers can infer the presence and characteristics of intervening objects
- Microlensing surveys provide valuable information about host stars and allow for measurements of planetary orbital parameters including mass and distance from their host star
- Low-cost space-based microlensing surveys could provide a comprehensive statistical census of extrasolar planetary systems with sensitivity down to 0.1 Earth masses and coverage ranging from 0.5 AU to infinity
- Gravitational microlensing offers unique insights into the properties and prevalence of extrasolar planetary systems, particularly low-mass planets at moderate separations from their host stars

## Summary

Gravitational microlensing is a powerful method for studying extrasolar planetary systems, as it allows for the detection of low-mass planets at separations of a few astronomical units (AU) from their host stars. Recent evidence from microlensing observations suggests that the most common type of exoplanet detected so far are "super-Earth" planets, which have masses of approximately 10 times that of Earth and are located at separations of a few AU from their host stars. In fact, the detection of two such super-Earth planets indicates that roughly one third of stars in our galaxy may have similar planets within the separation range of 1.5-4 AU. This prevalence is about an order of magnitude larger than that observed for gas-giant planets at these separations. To understand how microlensing enables the detection of Earth-mass planets at separations of 2-3 AU using ground-based observations, it is important to review the basic physics behind this method. Microlensing occurs when a foreground object, such as a star or planet, passes in front of a background star and its gravitational field causes a temporary magnification or brightening effect. By carefully monitoring these brightness variations, astronomers can infer the presence and characteristics of any intervening objects. Furthermore, microlensing surveys can also provide valuable information about the host stars themselves and allow for measurements of planetary orbital parameters including mass and distance from their host star. Looking ahead, there is potential for conducting low-cost space-based microlensing surveys that could provide a comprehensive statistical census of extrasolar planetary systems. Such surveys would have sensitivity down to 0.1 Earth masses and cover a wide range of separations ranging from 0.5 AU to infinity. Overall, gravitational microlensing offers unique insights into the properties and prevalence of extrasolar planetary systems, particularly with regards to low-mass planets at moderate separations from their host stars. With further advancements in observational techniques and the potential for space-based surveys, our understanding of these systems is expected to greatly expand in the future.