The angels have the ability to travel from heaven to earth and visa-versa . Not only that a lot of time has passed. This would be hard to understand if you're not familiar with the 3 ages taught by God and Christ. One place to start your study Jeremiah 4 : 19-. and 2nd Peter chapter 3.
The Bible dose not mention aliens....
The angels have free reign to do what they wanted . Those structures are not new, they are way old I'm sure, they made many things.
We are made in their image to looks like they do. We have done some space travel our selves as people. And have made many things in space. It follows simple logic that they would be able to do the same, and more then us.
2nd Kings chapter 2 :
[10] And he said, Thou hast asked a hard thing: nevertheless, if thou see me when I am taken from thee, it shall be so unto thee; but if not, it shall not be so.
[11] And it came to pass, as they still went on, and talked, that, behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven.
[12] And Elisha saw it, and he cried, My father, my father, the chariot of Israel, and the horsemen thereof. And he saw him no more: and he took hold of his own clothes, and rent them in two pieces.
2nd Kings 6:
15 And when the servant of the man of God was risen early, and gone forth, behold, an host compassed the city both with horses and chariots. And his servant said unto him, Alas, my master! how shall we do?
16 And he answered, Fear not: for they that be with us are more than they that be with them.
17 And Elisha prayed, and said, Lord, I pray thee, open his eyes, that he may see. And the Lord opened the eyes of the young man; and he saw: and, behold, the mountain was full of horses and chariots of fire round about Elisha...
Zechariah 6 You read here that these are sent from God Himself.
King James Version (KJV)
6 And I turned, and lifted up mine eyes, and looked, and, behold, there came four chariots out from between two mountains; and the mountains were mountains of brass.
2 In the first chariot were red horses; and in the second chariot black horses;
3 And in the third chariot white horses; and in the fourth chariot grisled and bay horses.
4 Then I answered and said unto the angel that talked with me, What are these, my lord?
5 And the angel answered and said unto me, These are the four spirits of the heavens, which go forth from standing before the Lord of all the earth.
6 The black horses which are therein go forth into the north country; and the white go forth after them; and the grisled go forth toward the south country.
7 And the bay went forth, and sought to go that they might walk to and fro through the earth: and he said, Get you hence, walk to and fro through the earth. So they walked to and fro through the earth.
8 Then cried he upon me, and spake unto me, saying, Behold, these that go toward the north country have quieted my spirit in the north country.
Job 40:
6 Then answered the LORD unto Job out of the whirlwind, and said,
7Gird up thy loins now like a man: I will demand of thee, and declare thou unto me....
Ezek.1 kjv
[1] Now it came to pass in the thirtieth year, in the fourth month, in the fifth day of the month, as I was among the captives by the river of Chebar, that the heavens were opened, and I saw visions of God.
[2] In the fifth day of the month, which was the fifth year of king Jehoiachin's captivity,
[3] The word of the LORD came expressly unto Ezekiel the priest, the son of Buzi, in the land of the Chaldeans by the river Chebar; and the hand of the LORD was there upon him.
[4] And I looked, and, behold, a whirlwind came out of the north, a great cloud, and a fire infolding itself, and a brightness was about it, and out of the midst thereof as the colour of amber, out of the midst of the fire.
[5] Also out of the midst thereof came the likeness of four living creatures. And this was their appearance; they had the likeness of a man.
[6] And every one had four faces, and every one had four wings.
[7] And their feet were straight feet; and the sole of their feet was like the sole of a calf's foot: and they sparkled like the colour of burnished brass.
[8] And they had the hands of a man under their wings on their four sides; and they four had their faces and their wings.
[9] Their wings were joined one to another; they turned not when they went; they went every one straight forward.
[10] As for the likeness of their faces, they four had the face of a man, and the face of a lion, on the right side: and they four had the face of an ox on the left side; they four also had the face of an eagle.
[11] Thus were their faces: and their wings were stretched upward; two wings of every one were joined one to another, and two covered their bodies.
[12] And they went every one straight forward: whither the spirit was to go, they went; and they turned not when they went.
[13] As for the likeness of the living creatures, their appearance was like burning coals of fire, and like the appearance of lamps: it went up and down among the living creatures; and the fire was bright, and out of the fire went forth lightning.
[14] And the living creatures ran and returned as the appearance of a flash of lightning.
[15] Now as I beheld the living creatures, behold one wheel upon the earth by the living creatures, with his four faces.
[16] The appearance of the wheels and their work was like unto the colour of a beryl: and they four had one likeness: and their appearance and their work was as it were a wheel in the middle of a wheel.
[17] When they went, they went upon their four sides: and they turned not when they went.
[18] As for their rings, they were so high that they were dreadful; and their rings were full of eyes round about them four.
[19] And when the living creatures went, the wheels went by them: and when the living creatures were lifted up from the earth, the wheels were lifted up.
[20] Whithersoever the spirit was to go, they went, thither was their spirit to go; and the wheels were lifted up over against them: for the spirit of the living creature was in the wheels.
[21] When those went, these went; and when those stood, these stood; and when those were lifted up from the earth, the wheels were lifted up over against them: for the spirit of the living creature was in the wheels.
[22] And the likeness of the firmament upon the heads of the living creature was as the colour of the terrible crystal, stretched forth over their heads above.
[23] And under the firmament were their wings straight, the one toward the other: every one had two, which covered on this side, and every one had two, which covered on that side, their bodies.
[24] And when they went, I heard the noise of their wings, like the noise of great waters, as the voice of the Almighty, the voice of speech, as the noise of an host: when they stood, they let down their wings.
[25] And there was a voice from the firmament that was over their heads, when they stood, and had let down their wings.
[26] And above the firmament that was over their heads was the likeness of a throne, as the appearance of a sapphire stone: and upon the likeness of the throne was the likeness as the appearance of a man above upon it.
[27] And I saw as the colour of amber, as the appearance of fire round about within it, from the appearance of his loins even upward, and from the appearance of his loins even downward, I saw as it were the appearance of fire, and it had brightness round about.
[28] As the appearance of the bow that is in the cloud in the day of rain, so was the appearance of the brightness round about. This was the appearance of the likeness of the glory of the LORD. And when I saw it, I fell upon my face, and I heard a voice of one that spake.
For an explanation to this I will send you a link in your mail ,, If you want.