Home > Science Objectives of SPICA

Revealing the Hidden History of the Universe

How was the universe born and how has it evolved ? How were the Earth and habitable living beings like us created ? To answer these questions is the ultimate objective of astronomy.

SPICA, a large-aperture (2.5 m) cryogenic space telescope, will tackle these questions through infrared studies of galaxy evolution and planet formation.

Fig. 1   A schematic view of SPICA

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Galaxy Evolution

Just after its birth in the Big Bang, 13.8 billion years ago, the Universe was extremely homogeneous and simple, consisting of only hydrogen and helium. How has it evolved into the present heterogeneous universe rich with a large variety of materials and even life ?

Through star formation activity in galaxies, the universe was enriched with matter such as the elements heavier than hydrogen and helium, organic matter, solid grains and dust. This material brought diversity to the universe. This picture, which was proposed a few decades ago, was observationally confirmed primarily by optical telescopes such as Subaru and Hubble. However, recent studies indicate that most of the Universe is hidden by thick dust clouds, and thus, is difficult to observe with optical telescopes.

Heavy metals, which are produced by stellar evolution in galaxies, are essential elements for the composition of the Earth, the Moon, and life including human beings. Understanding the process of enrichment of the Universe with heavy metals, solid grains and organic materials is a key needed to reveal the origin of our Galaxy (the Milky Way), the Solar System and the Earth. These materials are thought to be produced mostly in the "dusty era", when the Universe was full of dust blocking the optical light. Therefore, optical observations have not been successful in clarifying the whole process of their production.

SPICA, with its high sensitivity in the mid-to-far infrared wavelength range where dust absorption becomes relatively insignificant, reveals the process of star formation in galaxies including the Milky Way, and of formation of planetary systems like our Solar System.

Fig. 2   Overview of the process from the Big Band to the current Universe. SPICA reveals the evolution of the Universe with mid-to-far infrared observations.

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Planetary Formation

When and how were planets born ?

The discovery of exoplanets in 1995 had a major impact on astronomy as up to that time the existence of exoplanets had been long disputed. Since then, a great deal of observational and theoretical research tried to answer the question as to whether the Solar System and the Earth are unique in the Universe.

It has been known lately that a number of stars have one or more planets. Some of the planets are found to be located in habitable environment. In spite of many exoplanets being discovered, the conditions and mechanism of their formation still remain unexplained.

To address these issues, SPICA will observe protoplanetary disks where planets, like those in the Solar System, are thought to be formed. By examining the properties of the protoplanetary disks as a function of their ages, SPICA can uncover the formation and evolution of planetary systems.

Fig. 3   Imaginary view of a protoplanetary disk. Planets are thought to be formed in the disk,
as a result of successive collisions and subsequent mergers of solid materials in the disk.

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