During the last twenty-five years, astrophysical research has been oriented, with ever-increasing interest, to the discovery of exoplanets in the Solar System neighbourhood. After the first observation of an extrasolar planet in 1995, 51 Pegasi b, many others have been discovered: the 1st October 2018, a total of 3851 confirmed exoplanets were listed in the Extrasolar Planets Encyclopaedia (exoplanet.eu). The surprising number of recent discoveries has been made possible thanks to the large amount of spacecraft missions addressed for this purpose: today we can count 46 active missions and 4 additional missions are planned for the next future, from 2019 to 2026.
In this scenario, the research of extraterrestrial intelligent life-forms gains new hopes and possibilities. Even before the discovery of the first exoplanets, indeed, humanity understood that the probability to embody the only life-form in the Universe was not realistic, and perhaps not even heartening. In 1972, the first attempt to send a message to another possible civilization in the Universe has taken the form of a NASA space probe, named Pioneer 10. The message carried by this spacecraft, by its twin Pioneer 11 (launched in 1973) and by the following space probes, followed the idea of sending out of the Solar System some information about the human beings and human knowledges, and our position in the Galaxy. The first challenge of this kind of mission is to preserve the message throughout the time, by travelling inside a capsule for thousands of light years. The second challenge of this ambitious purpose is to find a way to send a message which could be received and deciphered from another intelligent life-form, living on an habitable planet somewhere in our Galaxy. Pioneer 10 and 11 carried their messages through drawings carved on metal plaques (solarsystem.nasa.gov/resources/706/pioneer-plaque), while the following Arecibo Message (1974) sent a radio message, containing a binary code with additional specific information, e.g., numbers, chemical elements, DNA. In 1977, another pair of twin spacecrafts left the Earth: Voyager 1 and Voyager 2, carrying the so called Golden Records (voyager.jpl.nasa.gov). Each Golden Record carried a collection of music songs and pictures, in addition to drawings carved on the metal cover, on the same line as Pioneer 10 and 11. The Voyager missions wanted to export from the Earth a representation of humanity, involving not only scientific information, but also arts, architecture, technology, animals and nature, through pictures and recorded songs. Now, let’s look briefly to some pros and cons of the two Voyager missions and their Golden Records, in order to introduce our project for a future space probe. The Voyager spacecrafts and the Golden Records have been built so that they can travel for thousands of years, meaning they may be able to reach an extrasolar planet. Nevertheless, the message sent is not supposed to be deciphered by a civilization which might probably be very different from ours. It would require also the instructions to decode all the carved drawings. The Golden Record is more addressed to carry a fingerprint of humanity, even if no one will be able to receive it, but it gives us a strong incentive to look ahead and carry out scientific research.
In the era of exoplanet surveys, in order to develop an idea for a new time capsule, we intend to move in a more realistic and feasible way. We came up with a project for a capsule for our message from Earth, which can be received and decoded by another intelligent life-form, although very distant from the Solar System. In addition to some essential informations, for which we provide the required decryption key, we wanted to send additional information about human knowledge and culture, with the aim of sending a human legacy to other possible habitants of the Universe.
We suggested a new “direct approach” to the challenge of extraterrestrial contact. Thanks to the space-based facilities, such as Kepler and recently Tess, we can benefit from many data regarding exoplanet properties, for instance, the chemical abundances of their atmospheres, the orbital parameters, and the various features of the stars around which they orbit: accurate stellar properties are crucial in determining exoplanet characteristics and Gaia DR2 (the ESA all sky star survey sci.esa.int/gaia) presents revised distances, luminosities, and radii for 1.6 billion stars.
For our purpose, we take into account only rocky planets, such as terrestrial-like and super-Earth planets orbiting in the goldilocks zone; in addition, because of the limited velocity of our spacecraft (up to ~1% of the speed of light), we are compelled to choose as targets only those planets located in the Keplerian field at distances varying from 40 to 1000 light-years from us.
Our new method consists in creating a plaque, which is inspired to the other ones sent with the Voyager missions. This plaque is composed by two sides, with drawings in relief, starting from the assumption that this alien civilization developed organs able to perceive touch and atmospheric pressure and at least at our technology level.
The first one involves a set of messages that would allow us to have a first interaction with an alien form of life. Such messages include:
A couple of dummies with mobile articulation would help the comprehension of the human anatomy, and a better understanding of the numerical representation used.
We could also be able to build a binary code based on the peak wavelength of the two stars: zero is represented by the peak of our sun and one is represented by its peak.
The second component consists of a collection of sounds, objects and concepts giving an illustrative idea of the human culture, achievements and spirit, trying to avoid those which may be interpreted as hostile messages.
After giving them essential rules on how to approach our message and assuming its comprehension, we could communicate a breath of human life.
Starting from the hypothesis that they might be able to use - at least - two senses, hearing and touch, they could sense us through sounds and objects too.
Thanks to a sort of touchable carillon (some reeds disposed in series), we would be able to let them reproduce parts of the most famous songs which would be surely recognized by any human being:
Humanity would not be the same without humans. Change is a crucial aspect of human life. Showing human looks in different life phases, would let them understand the multiple faces of our life, from birth to old age, through teenage years and adulthood.
On this side of the plaque, we would also reproduce DNA double helix structure and the Hydrogen atom, hoping that they would try to understand their meaning and its relevance for guarantee life on Earth.
Finally, the capsule has a double function: first of all, it protects the plaque from the interstellar space and makes the landing on the exoplanet safe. The second function is the capability of reflecting the star light isotropically, thanks to its spherical shape and its high albedo, set on the peak of their star spectrum: this property allows the probe to be visible through astronomical observation when in outer space. In addition, the capsule will contain isotopic ratios of characteristic elements of our Solar System (such as C and O), giving them the opportunity to understand the basic components of our planetary system and let them recognize the external origin of the probe.
Real application: TRAPPIST-1
TRAPPIST-1 is a dwarf star of ~0.09 solar masses, just slightly above the limit to ignite the nuclear fusion into the star core. Its ultra-cold surface temperature (~2500 K) sets its black body peak frequency in the infrared spectrum range, at shorter wavelengths than those visible by humans. Hence, both the symbol representing TRAPPIST-1 in the plaque and the time capsule shall be made by a material reflecting mostly the infrared light.
The peculiar property of this star is that it is surrounded by a planetary system consisting of seven terrestrial planets, a larger number than that detected in any other discovered system. In particular, three Earth-sized planets orbiting the dwarf star are considered to be within its habitable zone. These features currently make TRAPPIST-1 system the ideal testing target for any mission that aims at making contact with extraterrestrial civilizations. In addition, its distance from the Sun (~40 light-years) is such to assess that the probe carrying the message will reach the system in a time short enough to hypothesize that our civilization will still be inhabiting Earth and will have possibly developed an advanced technology and culture. As an example, if we consider a space probe moving at 1% of the light speed (corresponding to four times the fastest speed currently reached by a human-made spacecraft), the time needed to reach TRAPPIST-1 is about 4000 years.
WE WERE HERE
Go beyond limits... human limits. That’s what inspired us.
All the collected information, sounds and human features, would allow a first contact with an alien civilization and, more over, would let humanity have a “backup” system of the human passage, as Armstrong did on the Moon with his steps.
This is our legacy. Our legacy to the Universe, despite what could happen to our Earth and our Solar System in next future.
Thanks to this plaque, we could send a physical and authentic proof of what we were in a specific moment of time.
This is the proof that living beings, whose material existence relies on water and Carbon, whose founding characteristics are intelligence and emotions, do existed.
SpaceApps is a NASA incubator innovation program.