Frequently Asked Questions
The most-asked questions about exoplanets found by imaging and microlensing.
What does 'exoplanets found by imaging' actually mean?
Direct imaging means a telescope literally captures light from a planet orbiting a star other than the Sun, separating the planet's glow from its host star's overwhelming glare. It is the only method that lets us photograph an exoplanet and, in some cases, probe its atmosphere with spectroscopy.
How does gravitational microlensing detect planets?
When a foreground star and its planet happen to pass almost directly in front of a more distant background star, gravity bends and amplifies the background light into a temporary brightening. The planet's small gravitational tug creates a brief anomaly in that light curve, revealing its presence even though the planet itself is never seen.
How do imaging and microlensing differ from the transit or radial-velocity methods?
Transit detection watches for a planet crossing its star's disk, while radial velocity tracks the star's tiny wobble caused by an orbiting body. Imaging and microlensing instead catch the planet's own light or its gravitational fingerprint, making them especially good at finding planets at wide orbital distances where transits are rare.
Who are some of the most associated names with these discovery methods?
In direct imaging, instrument teams behind SPHERE, HiCIAO, and the VLT/Keck observing programs are frequently cited, along with researchers like Christophe Morlo and David Lafrenière. In microlensing, the OGLE, MOA, and KMTNet survey collaborations—driven by figures such as Andrzej Udalski and the broader microlensing community—have produced the bulk of detections.
Roughly how many exoplanets have been confirmed by imaging and microlensing combined?
As of the mid-2020s, direct imaging has confirmed on the order of 25–30 planets, and microlensing has confirmed well over 100. Together they represent a small but scientifically rich slice of the total known exoplanet population.
What are some of the most famous planets found by these techniques?
51 Eridani b was among the first directly imaged exoplanets, and Beta Pictoris b became iconic as one of the first clearly captured in visible light. In microlensing, OGLE-2005-BLG-390Lb was an early 'cold Jupiter' detection, while events like KMT-2021-BLG-1854Lb have pushed the method toward Earth-mass worlds.
Where should a newcomer start if they want to follow these discoveries?
The original discovery papers on arXiv or in journals like The Astronomical Journal and The Astrophysical Journal provide the primary data and figures. For a more accessible narrative, the ESO press pages, the NASA Exoplanet Archive, and the OGLE and MOA project websites offer image galleries and plain-language summaries.
What can these methods reveal that transit or radial velocity cannot?
Imaging lets us study a planet's reflected or thermal emission and, with high-resolution spectroscopy, its atmospheric chemistry. Microlensing is uniquely sensitive to planets at very wide separations, to low-mass planets around faint or distant stars, and even to free-floating planets that have no host star at all.
What are the main limitations of direct imaging and microlensing?
Imaging is constrained by the enormous brightness contrast between star and planet, so it preferentially finds young, massive, widely separated worlds and demands very large apertures or coronagraphs. Microlensing events are one-time, non-repeatable, and a single light curve only partially constrains the planet's true mass and orbital distance.
What upcoming facilities or missions will expand these searches?
The Nancy Grace Roman Space Telescope will use microlensing to survey the Galactic bulge for Earth-mass planets at a scale no ground survey can match. On the ground, the Extremely Large Telescope and next-generation interferometers aim to image and characterize more directly imaged planets, while KMTNet continues real-time monitoring of microlensing events.