Gaia: science essays
In these short (mostly 2-page, weekly) 'essays', I have picked out some of the scientific highlights of the Gaia mission as they are emerging, or as they caught my attention. They offer a somewhat chronological snapshot of some of the discoveries that Gaia is making across all of astronomy. I've also included some essays on related topics, including the history of astrometry, and some more technical, managerial, or developmental aspects of both the Hipparcos and Gaia missions. In each, I have included a footnote DR1, DR2, EDR3, DR3, etc to indicate which of the (latest) data releases the essay refers to (described in essays #10 and #76), with DR0 signifying technical or historical material not connected with any specific data release. Who are they written for? Anyone who might have a general interest in science and astronomy, including amateur astronomers, young scientists starting out on their careers, mid-career scientists looking in on Gaia for the first time to get a feeling of what is possible, and specialists looking in from different areas of astronomy, or physics more generally. Click on the access PDF icon to access the file. Only a few references are included, and these are 'discreetly' hyperlinked for those who want to read more... where references appear in the form (Einstein 1908) or www.gaia.com, clicking on the text (even though generally not highlighted!) should lead to the relevant online article. Essays 1-236 were published weekly, 237-241 monthly, and 242 onwards every two weeks. In a few cases, I've recorded an interview on the subject (see science interview page).
New: This table page lists all essays, updated to the end of June 2026 (1–235 inclusive), in tabular form. It includes a simple search on the title field.
New: These annual compilations are in both pdf and 'flipbook' form (open in new page; larger files as a download):
pdf:
flipbook:
New: The material in essays 1–239 is broadly included in my review "Space astrometry with Gaia: Advances in understanding our Galaxy" published in Physics Reports, Volume 1150, pp. 1–229 (January 2026): available here
New: This Gaia Science Tree (v4.0, June 2026) presents essays 1–235 (Jan 2021–Jun 2026) as a hyperlinked "mind map"
* all end-nodes are hyperlinked to the given essay number (links are to "legacy" copies at the CERN-Zenodo site)
* catalogue content topics are at top right, background material at bottom left, otherwise moving "outwards" clockwise in the diagram
* I have prepared this as a didactic tool. Please feel free to make use of it as you wish
I have converted Essays 1–130 into audio "discussion-type" podcasts, entirely using generative AI. They are available at my Gaia Essay YouTube channel, and I describe their construction in Essay 227.
Please make use of this subscribe page to receive an email (usually Monday) when each new essay is published
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254. Planet engulfment - and the Sun
Gaia is probing some of the ideas related to planetary engulfment
Binary systems offer an important testing ground of the idea that some stars may have engulfed one of their orbiting planets. Specifically, if one component is unusually rich in refractory elements, this might point to a past planetary engulfment. Gaia is making a number of contributions to this debate.
29 June 2026
253. The oldest stars
Are the oldest stars older than the Universe itself?
For a handful of stars, current models of stellar structure and evolution provide age estimates which sit uncomfortably close to our estimate of the age of the Universe itself. Larger statistical samples constructed from the accurate and homogeneous Gaia data are providing a more robust `cosmic clock'.
15 June 2026
252. The Great Wave
A new structural feature in our Galaxy's disk
The Galaxy disk is no longer thought of as simply `flat'. In the 1950s it was shown to be warped. Gaia has revealed other dynamical and morphological structures, including the `phase-space spiral' and the Radcliffe Wave. Recent studies have revealed a much vaster distortion, the Great Wave.
1 June 2026
251. Binary open clusters
Many new insights into binary clusters
The first hints that open clusters are sometimes found in pairs emerged in the 1970s. Today, binary clusters provide insights into cluster formation, star formation, and tidal interactions. New discoveries and detailed kinematic studies with Gaia DR3 are consolidating this picture.
18 May 2026
250. An AI ‘big picture’ of Gaia science
An AI-based synthesis of Gaia science to date
Stefan Jordan, a member of the Gaia DPAC collaboration at the University of Heidelberg, recently used NotebookLM to synthesise my entire collection of essays to provide an overview of Gaia science divided into five subject areas. I reproduce this synthesis here.
4 May 2026
249. The Greater Pleiades Complex
Revealing the vast spatial extent of the associated star-formation region
Identifying stars which have escaped from open clusters since their birth is important in clarifying many details of the underlying star formation and evolution processes. A recent study combines the Gaia data with stellar rotational data from TESS, to more securely identify young escaping members of the Pleiades out to larger distances than has been possible using the Gaia data alone.
20 April 2026
248. Exoplanet host stars
More precise radii of exoplanets and their host stars
A recent study using Gaia DR3 has provided improved radii for 2573 exoplanet host stars and their associated 3556 exoplanets. Amongst the scientific findings is the confirmation of the `radius valley', first identified in the Kepler data, and attributed to the host star's X-ray/UV radiation. This results in sub-Neptunes losing their H/He envelopes and emerging as rocky super-Earths.
6 April 2026
247. Tumbling asteroids
Understanding why and how some asteroids tumble
Multi-epoch photometry can identify the rotation period and spin-axis direction of solar system bodies. A gap in the period-diameter diagram of asteroids reveals a concentration of short-period `tumblers', those rotating in a non-principal axis state. A recent Gaia study provides a detailed model of the underlying physics: how they got into a tumbling state, and their distribution in the period-diameter diagram.
16 March 2026
246. Star formation episodes§
The star formation history of our Galaxy
Four recent studies have exploited the Gaia colour-magnitude diagrams to study our Galaxy's evolutionary history. These are focused on (1) the star-formation history of the solar neighbourhood; (2) the evolution of the thin and thick disk populations; (3) the age and metallicity of GSE stars near the Sun; and (4)the age distribution of stars of the inner Milky Way.
2 March 2026
245. Hypervelocity stars: part 3
A neat explanation for the distribution of hypervelocity stars
A puzzling feature of the known hypervelocity stars is their particular distribution on the sky. A recent Gaia DR3 study provides an explanation: such stars originate both from the supermassive black hole at our Galaxy's centre, as well as from a supermassive black hole in the LMC, whose observed population is boosted by the LMC's orbital motion.
16 February 2026
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