"Small-JASMINE": Japan Astrometry Satellite Mission for INfrared Exploration

About Small-JASMINE

Main science objective of Small-JASMINE is "Galactic Center Archaeology", to understand the formation and evolution history of our Galaxy, the Milky Way. Small-JASMINE will measure the precise position and motion of stars in the Galactic nucleolus region, which is the core of the Milky Way. Unveiling the spatial distribution and motions for stars in the Galactic center, where the generations of stars are retained since the beginning of the Milky Way, will enable us to uncover the formation and history of the Milky Way. Understanding the formation processes of the Milky Way will also help us to understand the formation of the other galaxies.

To achieve this science objective, Small-JASMINE is designed as follows.

In space:
Small-JASMINE will be a space astrometry mission, and the nominal operation period is planned to be 3 years.
Near Infrared astrometry:
Small-JASMINE will measure the precise distance and motion of stars in near-infrared band (1.1-1.7 microns).
Targeting Nuclear Bulge (Galactic Center Region):
Small-JASMINE will achieve the accuracies of 25 micro arcsec in annual parallax (distance) and 25 micro arcsec/yr in proper motion (tangential velocity) measurement for stars in the Galactic center.
Catalog public release:
The final catalog of the position and motions of all the stars observed by Small-JASMINE will be publicly released, which will be valuable for wide areas of sciences in astronomy.

Keyword: Astrometry, Annual parallax, Proper motion, Galactic Nuclear Bulge (Galactic Center Region), Galactic Center Archaeology

Scientific Objectives of Small-JASMINE

"Galactic Center Archaeology"

Structure of the Galactic nuclear bulge and formation epoch of the Galactic bar.

The world-first near-infrared Galactic center astrometry mission, Small-JASMINE will reveal the detailed structure of the Galactic center region, so-called Galactic nuclear bulge, whose structure and the formation history are still mystery and veiled with the heavy dust extinction. One of the interesting structures in the Galactic center region is a Galactic nuclear disk, which is considered to be formed when the Galactic bar formed. Small-JASMINE will uncover the age distribution of the Mira variable stars in the Galacitc nuclear disk, and identify the formation epoch of the nuclear disk, and therefore the formation epoch of the Galactic bar.

Gas inflow to a super-massive black hole

There is a super-massive black hole (SMBH) with about 4 million times more massive than the Sun at the center of our Galaxy. However, how the SMBH is growing is not known. Small-JASMINE will reconstruct the mass distribution, non-axisymmetry and rotation properties of the Galactic nuclear bulge. From these properties we will study how and how much the gas is falling into the Galactic center and feeding the SMBH.

Relic of super-massive black hole formation

One of the potential formation scenarios of the SMBH is a successive mergers of massive black holes. If the SMBH of the Milky Way formed through this mechanism, such mergers must strongly impact on the kinematics of the stars in the Galactic center region. Small-JASMINE will measure the precise position and motion of stars in the Galacic center region, which would be enough to tell such impact, and therefore Small-JASMINE will tell us if or not our SMBH formed via mergers.

Hidden Star Clusters

The accurate proper motion, tangential motion in the sky, measurements of stars in the Galactic center enable us to find hidden star clusters not possible to be identified with photometric surveys. The proper motion data enable us to identify star clusters, even the ones dissolving, as groups of stars moving coherently. The orbit and age of the star clusters will help us to uncover the formation and evolution history of the Galactic nuclear bulge, because all stars are believed to born in star clusters.

Hyper velocity star

There are some stars whose velocity is too fast, hyper velocity stars, to be explained with the normal star formation process. One of promising origins of the hypervelocity stars is a population kicked out from the strong gravitational influence of the SMBH in the Galactic center. If Small-JASMINE found such hyper velocity stars to be consistent with this scenario in the Galactic center, it provides a direct evidence of the SMBH origin of hyper velocity stars.

Astrometric Gravitational micro-lensing

Astrometric gravitational micro-lensing is a phenomenon that the position of a background star changes when a compact object, such as a stellar mass black hole, passed through between the background stars and us. Small-JASMINE will monitor such micro-lensing events, which will tell us the number and masses of black holes.

"Extra Targets Candidates when the Galactic center is not observable"

Small-JASMINE will make the targeted observations for the other sciences, on which unique capability of Small-JASMINE can provide strong impact, in summer and winter when the Galactic center is not observable. The selection of the target is on-going. The candidates are listed below.

Exoplanets (Extrasolar Planets)

Planets around a star can gravitationally attract the host star, and the position of the star in the sky slightly shifts depending on the relative positions of the planets. This can be observed as periodic positional shifts, and enables us to find new exoplanets using astrometry. Exoplanets can be found with the transits seen in the light curve of the host star, i.e. the periodic dimming of the stellar light when a planet passes the front of the star. Small-JASMINE especially targets M-type main-sequence stars, which is a low temperature low mass star, but bright in near-infrared. Because M-type main-sequence stars are intrinsically less bright, the so-called habitable zone of the planet, where the life is likely to be able to survive, is closer to the star and therefore the orbital period of habitable planets is short. Therefore, M-type main-sequence stars are the ideal target to discover a habitable planet. Small-JASMINE can provide time-series near-infrared photometry for M-type main sequence stars, and therefore Small-JASMINE is an ideal satellite to detect habitable planets around M-type main-sequence stars.

Other potential targets

Compact objects, e.g. Cygnus X-1. Variable stars. Star forming regions.

Mission overview

Technical Challenges

Astrometric observations in space

Ultra-stable telescope

Innovative data analysis technique

International Supports

Domestic Supports

Schedule and Plan