Interstellar space biology via Project Starlight

Abstract

Our ability to explore the cosmos by direct contact has been limited to a small number of lunar and interplanetary missions. However, the NASA Starlight program points a path forward to send small, relativistic spacecraft far outside our solar system via standoff directed-energy propulsion. These miniaturized spacecraft are capable of robotic exploration but can also transport seeds and organisms, marking a profound change in our ability to both characterize and expand the reach of known life. Here we explore the biological and technological challenges of interstellar space biology, focusing on radiation-tolerant microorganisms capable of cryptobiosis. Additionally, we discuss planetary protection concerns and other ethical considerations of sending life to the stars.

Keywords: Cryptobiosis; Directed energy propulsion; Interstellar propulsion; NASA starlight; Planetary protection; Space biology.

Fig. 1.. Directed Energy Propulsion of a Light Sail.

(a) A light sail and payload propelled into interstellar space by directed energy laser propulsion. Emitted photons from a standoff laser array on the surface of the Earth (space-based laser arrays are also possible) impart momentum on the sail by reflection so as to accelerate the spacecraft up to relativistic speeds. Artist’s rendition. (b) The laser array is composed of many small, modular sub-elements which can be articulated, switched off, and added so as to enable a large mission space. As the capability of directed energy propulsion grows, relativistic flight will become possible.

Fig. 2.. Metabolic rate (MR) and mass for various groups of living organisms.

Despite the vast diversity of species, we observe a near universal energy requirement per unit mass of tissue. This generalization excludes species capable of cryptobiosis (such as tardigrades, brine shrimp, and Chironomidae), which exhibit virtually no metabolic activity while in a state of suspended animation, making them better suited for interstellar flight [–52].

Fig. 3.

In the case of gamma radiation, most organisms exhibit LD₅₀ (median lethal dose) values on the order of 10¹–10² Gy; however, certain nematode, fungi, rotifer, tardigrade, bacterial, and archaeal species demonstrate much higher tolerances (~10³–10⁴ Gy) [–77]. Even across species, large differences in LD₅₀ values exist, as can be seen between the three represented tardigrade species M. tardigradum, R. coronifer, and H. dujardini.