Space based Microlensing surveys combining Roman and Euclid – SPACE-MLENS

Studying cold planet demographics via microlensing and probing the nature of Dark Energy with Cosmic Shear and Baryonic Acoustic Oscillations, share the same requirements of a space-based infrared wide field imager. Microlensing has been listed as additional science of Euclid since 2007 following our proposition. The 2010 US decadal survey joined these two themes when creating the WFIRST space mission and commented that it is “the only platform in the coming decades that can produce a statistical census of planetary occurrence as a function of orbital separation and mass, from terrestrials to gas giants, beyond 1 AU”. Rebranded Roman, this 2.4-meter space telescope, equipped with a wide field IR imager, will launch early 2027. The current baseline, called RGES (Roman Galactic Exoplanet Survey), is a ~6x72-day observation of the galactic Bulge with publicly available data with no proprietary period. Microlensing has a long tradition of operating in a coordinated way, fostering emulation through internal cooperation-competition, rather than separate competing teams. Therefore, two of us joined forces with 42 scientists in the Project Infrastructure Team (RGES-PIT) proposal to NASA. Meanwhile, under our impulse, ESA, NASA and the Euclid Board has agreed to do precursor observations of 4.5 square deg of the Roman fields to help to better define the Roman survey, and provide references for source-lens proper motion which will become mass constraints. With Euclid precursor observations (scheduled in October 2024), Roman will provide mass measurements from year-1 instead of waiting for several years.

The objective of SPACE-MLENS is to enhance the RGES-PIT, be in the front line for analysis of Euclid data (to refine the choice of the survey field and mass measurement), development of key workpackages, and have an important role in the first campaign (late 2027-early 2028) that will deliver 200+ planets down to the mass of Mars, and probably 100+ sub-neptune free-floating planets.


Our ingredients are: Euclid precursor observations of Roman fields, a close collaboration with the Japanese PRIME team which monitors with an 8k8k IR camera a field in the Roman paw print, the University of Tasmania with capacity of IR monitoring of PRIME planetary events, development of key work packages within the RGES-PIT (survey, mass measurement, modeling).

The immediate objectives are:

1/ Analyzing the VIS Y J H data of the 4.5 deg^2 Euclid survey of the Roman microlensing fields. Provide detailed catalogues of photometry, astrometry, reddening maps. It will help to define the adopted 2 deg^2 fields for the RGES.

2/ Providing source-lens relative proper motion and flux ratio estimates for old microlensing events from this field and derive a mass function for the lensing population.

3/ Determining the structure of the Roman line of sight using Euclid and larger field of view surveys from VVV and PRIME (1.8m telescope in South Africa with an 8k IR camera), planetary events alerted by PRIME and monitored in IR, GAIA and galactic models to help to define the priors for microlensing light curve modelling in Roman fields.

4/ Follow up of planetary events from PRIME in the field of view of Roman (using IR monitoring capability), testing modelling of light curves with these new constraints about the line of sight, extinction, distances, lens population.

5/ Developing and delivering an open source code for optimal measurements of source-lens relative motion with Euclid and Roman. Delivering a planetary microlensing code to model planetary systems taking into account the constraints from relative source-lens proper motions and flux ratios using GPU.

6/ Analyzing the first observing season of RGES to have a first estimates of planet demographics.

7/ Obtaining agreement for simultaneous L2-L2 Euclid/ESA-Roman/NASA space observations for measuring the mass for a significant fraction of telluric free-floating planets thanks to parallax effects.